Speaker 1: Get in touch with technology with tech Stuff from how
Speaker 1: stuff Works dot com. Hey there, and welcome to tech Stuff.
Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with
Speaker 1: how Stuff Works in I Love all Things Tech. And
Speaker 1: in our last episode, I traced the history and evolution
Speaker 1: of forensic science and how it kind of grew up
Speaker 1: of out of a bunch of other kind of parallel
Speaker 1: developing areas of investigation. And today we look at forensic
Speaker 1: science as a collection of these various techniques and technologies
Speaker 1: to to investigate crime and to solve crime. So today
Speaker 1: I wanted to look more at some of the actual
Speaker 1: tech use. I was kind of light on the tech
Speaker 1: in the last episode. I was talking more about the
Speaker 1: evolution of the ideas behind it, because that really informs
Speaker 1: how the tech itself evolved. And today we're gonna look
Speaker 1: a little more closely at that now. In the last episode,
Speaker 1: I did mention the comparison microscope, that is a microscope
Speaker 1: that is typically a pair of light microscopes. Isn't the
Speaker 1: microscopes that use light as the medium to magnify stuff
Speaker 1: into your eyeballs, So the companion or comparison microscope is
Speaker 1: a pair of these right, it's it's essentially side by
Speaker 1: side two light microscopes that are actually bridged together, but
Speaker 1: on casual glance it looks almost like kind of binoculars
Speaker 1: in a way. And here's a quick rundown on how
Speaker 1: light microscopes work so that you can understand what a
Speaker 1: comparison microscope is able to do. A basic upright light
Speaker 1: microscope the kind you might see in a high school
Speaker 1: lab or even you know, I guess elementary school and
Speaker 1: middle school labs. Now when when I was a student,
Speaker 1: they didn't let a play with us until we were
Speaker 1: essentially high schoolers. But you are probably familiar what what
Speaker 1: these look like. It's that little upright microscopees gun. I
Speaker 1: piece at one end has a little platform it's called
Speaker 1: the stage where you would put a sample to h
Speaker 1: to examine. Well, they're called light microscopes because they have
Speaker 1: a light source at the base. Typically, your basic upright
Speaker 1: light microscope does that shines light up through a sample
Speaker 1: so that you can see it when you're looking through
Speaker 1: the I piece above. The light source is a special
Speaker 1: lens called a condenser. Now, the condenser's purpose is to
Speaker 1: redirect a divergent beam of light from a light source
Speaker 1: into a converging beam to illuminate a sample. So essentially
Speaker 1: you're focusing light on the smaller area that the sample
Speaker 1: itself will sit on, and of course that is on
Speaker 1: the part of the microscope that's called the stage. The
Speaker 1: microscope has what is called an objective lens that's near
Speaker 1: the end opposite where you put your eye, so this
Speaker 1: is the end that's closest to the sample. Uh. The
Speaker 1: lens that's close to your eye, by the way, is
Speaker 1: fittingly called the ocular lens. So the objective lens and
Speaker 1: the condenser are aligned to focus on the same spot
Speaker 1: of a sample, so the light from the condenser is
Speaker 1: hitting the same region of a sample that the objective
Speaker 1: lens is focused on. The job of the objective lens
Speaker 1: is to gather light from the point of observation and
Speaker 1: focus that light to produce a real image. Objective lenses
Speaker 1: are in stuff like cameras and telescopes to they're not
Speaker 1: just in microscopes. The lenses in the eyepiece of the
Speaker 1: microscope do the majority of the actual magnification. So with
Speaker 1: light microscopes you can sometimes swap out the objective lens,
Speaker 1: but rarely can you swap out the eye piece. Uh.
Speaker 1: The reason you would swap out the objective lens is
Speaker 1: because it does affect the magnification somewhat. A more flat
Speaker 1: objective lens will have a lower magnification than a rounder
Speaker 1: objective lens. This is all due to the physics of optics,
Speaker 1: which I'm not going to go into here because without
Speaker 1: visual aids, I would be struggling to describe them accurately.
Speaker 1: The purpose of swapping out those objective lenses is to
Speaker 1: focus on either larger or smaller areas of a sample.
Speaker 1: So if you need to look at really small regions
Speaker 1: of a sample, you'll want a rounder objective lens, and
Speaker 1: this will let you look at the very tiny regions
Speaker 1: of a sample. A comparison microscope is, like I said,
Speaker 1: a pair of these light microscopes and allows you to
Speaker 1: view two samples at the same time. That lets you
Speaker 1: compare those two samples, and you can eliminate the necessity
Speaker 1: to rely upon memory when comparing one sample with another,
Speaker 1: and in the case of forensics, that's incredibly important. You
Speaker 1: might be comparing a bullet that was retrieved from a
Speaker 1: crime scene with a bullet that you have fired from
Speaker 1: a firearm that you suspect was used at that crime scene.
Speaker 1: So you want to see if these two bullets were
Speaker 1: in fact fired out of the same firearm, and you
Speaker 1: want to be able to compare the markings on bullet
Speaker 1: one versus bullet Too. But if you were just having
Speaker 1: to swap them out underneath the same microscope, you would
Speaker 1: have to remember, all right, well, the markings I saw
Speaker 1: on bullet one, do they match up to what I'm
Speaker 1: seeing now in bullet too. With a comparison microscope, you
Speaker 1: can look at them side by side in real time,
Speaker 1: and that's much more reliable than looking at one sample
Speaker 1: than removing it from the microscope, putting in a second
Speaker 1: sample and then saying, huh, I think this looks the same.
Speaker 1: So it it took a lot of ambiguity out of investigation. Now.
Speaker 1: Light microscopes are really useful, but sometimes you gotta go
Speaker 1: a little further than what light microscope can do. They
Speaker 1: have limitations on the amount of magnification they can provide,
Speaker 1: and that's where you might want to up your game
Speaker 1: a bit go with something like a scanning electron microscope.
Speaker 1: Those microscopes can magnify a sample up to three hundred
Speaker 1: thousand times. It is an enormous amount of magnification. And
Speaker 1: a scanning electron microscope can also have depth of field,
Speaker 1: like really good depth of field, to the point where
Speaker 1: you will end up with an image that is almost
Speaker 1: three D in nature. The s c M can or
Speaker 1: scanning electron microscope can tell researchers a lot about the
Speaker 1: composition of a sample, so not just what it looks like,
Speaker 1: but the stuff that it's made out of. So we
Speaker 1: should talk about how these work because it's simple to
Speaker 1: say scanning electron microscope, but what does that really mean. Well,
Speaker 1: back in two scientists developed a precursor to this, called
Speaker 1: the transmission electron microscope or t e M, and that
Speaker 1: microscope would direct a beam of electrons through a sample
Speaker 1: to create a projectable image. Scanning electron microscopes followed soon afterward.
Speaker 1: They were developed in nineteen five, just a couple of
Speaker 1: years later, and initially they didn't get a whole lot
Speaker 1: of support in the scientific community. Uh, partly because the
Speaker 1: transmission electron microscopes that just come out we're already seen
Speaker 1: to have covered that territory. Scientists are saying, well, why
Speaker 1: should we spend money developing this new technology. We already
Speaker 1: have this other one that seems to do the same thing. Ultimately,
Speaker 1: scanning electron microscope showed that they had features that made
Speaker 1: them appealing on their own. So your basic scanning electron
Speaker 1: microscope consists of the following parts, and it is very
Speaker 1: different in many ways from a light microscope. You're not
Speaker 1: looking through an eyepiece the way you would with a
Speaker 1: light microscope. First of all, the entire guts of the
Speaker 1: scanning electron microscope are inside a vacuum chamber. The microscope
Speaker 1: itself is sealed in such a way that there is
Speaker 1: a vacuum inside of it. And it has to be
Speaker 1: like that because you're using electrons as you're scanning medium.
Speaker 1: You don't want to have any interference from particles or
Speaker 1: even air molecules. Those could be uh obstacles for an
Speaker 1: electron beam and it would throw everything off if you
Speaker 1: in fact had particles or air inside the microscope. So
Speaker 1: it needs to be a vacuum. The really important element,
Speaker 1: actually all of them are really important, but the business
Speaker 1: element of the scanning electron microscope is the electron gun.
Speaker 1: These are devices that produce a beam of electrons. It's
Speaker 1: really not that different from old CRT televisions. Those have
Speaker 1: electron guns that fire electrons at a phosphorus screen to
Speaker 1: create the light that you would see on an old television,
Speaker 1: but in this case, the electron gun creates a beam
Speaker 1: of electrons to scan your sample. The most common version
Speaker 1: of the electron gun that you will find is the
Speaker 1: thermionic gun, which, as the name implies, has to do
Speaker 1: with heat, right, thermal thermionic. So you heat up a filament.
Speaker 1: You typically would use something like tungusten because as a
Speaker 1: very high melting point, you heat it up really, really
Speaker 1: really hot. And when you do that, when you pour
Speaker 1: energy into it, you help it shed electrons. I've talked
Speaker 1: about this before, where pouring energy into an atom means
Speaker 1: that you're energizing those electrons. Electrons typically orbit and atoms
Speaker 1: nucleus in energy shells, and by boosting the energy of
Speaker 1: those electrons, they moved to higher and higher shells outside
Speaker 1: of that nucleus, and if you pour in enough energy,
Speaker 1: you can strip the electron away from the atom entirely.
Speaker 1: So that's what you do with these electron guns. The
Speaker 1: filament heats up to this incredible temperature and starts to
Speaker 1: shed off electrons. And then you aim those electrons at
Speaker 1: a sample. The other type of electron gun, by the way,
Speaker 1: is the field emission gun, that uses strong electrical fields
Speaker 1: to strip electrons away from their associated atoms. Electron guns,
Speaker 1: whether they're thermionic or field emission guns, are located on
Speaker 1: one end or the other of a scanning electron microscope.
Speaker 1: They're either at the very top or at the very bottom.
Speaker 1: Either way, they're doing the same thing. The lenses in
Speaker 1: a scanning electron microscope are not optical lenses. They're not
Speaker 1: ground glass lenses. The lenses in the scanning electron microscope
Speaker 1: are actually magnets because magnets can shape the path of electrons.
Speaker 1: Electrons have a charge, so using magnets you can attract
Speaker 1: or repel electrons. This is how particle accelerators like the
Speaker 1: large hadron collider work. They use these powerful electro magnets
Speaker 1: to control the beam of charged particles protons or electrons.
Speaker 1: The scanning electron microscope uses magnets to focus the beam
Speaker 1: of electrons and control them and direct them to where
Speaker 1: they need to go in order to scan a sample.
Speaker 1: The scanning electron microscope also has a sample chamber. That's
Speaker 1: where you actually place the specimen that you are scanning,
Speaker 1: and since we're talking about crazy levels of magnification here,
Speaker 1: you need that sample to be super still. Any movement,
Speaker 1: any vibration is going to be magnified dramatically and it's
Speaker 1: going to corrupt your results. So you want it to
Speaker 1: be very stable, and typically that means insulating it against
Speaker 1: all vibrations as much as you can. So if you
Speaker 1: were to go to visit like a forensics lab, and
Speaker 1: let's say it's a huge forensics lab, maybe it's an academy,
Speaker 1: and it's got multiple floors, chances are you're going to
Speaker 1: find the scanning electron microscopes on the ground floor, because
Speaker 1: going up more than just the ground floor could potentially
Speaker 1: introduce vibrations to your sample chamber and that would throw
Speaker 1: off your results. The scanning electron microscope also has detectors.
Speaker 1: Right you're you're blasting a sample with electrons, you have
Speaker 1: to have detectors to pick up the response of that,
Speaker 1: and those detectors include stuff like secondary electron detectors. Those
Speaker 1: are detectors that can actually register electrons from the sample itself. So,
Speaker 1: in other words, you're bombarding the sample with electrons from
Speaker 1: your electron beam. Sometimes that dislodges electrons from the surface
Speaker 1: of the outer surface of the sample, so the secondary
Speaker 1: electron detectors can pick those up. But other detectors will
Speaker 1: include back scatter detectors or X ray detectors. So when
Speaker 1: you are scanning a specimen, the electron beam moves over
Speaker 1: the surface of the object, and to do that, the
Speaker 1: scanning electron microscope uses what are called scanning coils. These
Speaker 1: are magnetic field generators that use fluctuating voltage to create
Speaker 1: the magnetic field, and the scanning electron microscope uses that
Speaker 1: to manipulate the electron beam. The coils direct the beam
Speaker 1: across the specimen in a very tight grid like pattern,
Speaker 1: so up and down, left and right, to get every
Speaker 1: single point on the surface of that specimen. That does
Speaker 1: dislodge electrons from the surface of the specimen in unique patterns,
Speaker 1: so the secondary detector attracts those scattered electrons and then
Speaker 1: registers those electrons as different levels of brightness on a monitor.
Speaker 1: So the intensity of the brightness that you see in
Speaker 1: the image will correspond with the number of electrons that
Speaker 1: hit the detector. The detector quote unquote knows where secondary
Speaker 1: electrons come from based upon the scanning beam's position, and
Speaker 1: this can be shown in an optical image on a
Speaker 1: video display. So think of for for the purposes of visualization,
Speaker 1: imagine a laser beam it's hitting a single point on
Speaker 1: a piece of cloth, let's say, And then imagine that
Speaker 1: you have a sensor that can pick up when electrons
Speaker 1: are being shot off by this piece of off. So
Speaker 1: we're thinking of a laser beam as that's the electron beam.
Speaker 1: We're just imagining it as a laser beam. You move
Speaker 1: the laser beam across the sample, and the detector is
Speaker 1: constantly picking up these electrons as they are shot off
Speaker 1: by the sample. And because this is all happening at
Speaker 1: essentially the speed of light, I mean, we're talking super fast,
Speaker 1: you know where those electrons are coming from, because you
Speaker 1: know what part of the sample the beam has just
Speaker 1: made contact with. And that ends up being transmitted to
Speaker 1: a computer system that interprets that and plots it as
Speaker 1: pixels points of light on the monitor, and then you
Speaker 1: get the computer image of what the scanning electron microscope
Speaker 1: just scanned. It's pretty darn cool. Backscattered electrons are those
Speaker 1: from the beam that reflect off the surface of the
Speaker 1: specimen and a detector can pick up those as well,
Speaker 1: and in a similar way constructive image. So backscatter. Those
Speaker 1: are electrons that came from the electron beam, not we're
Speaker 1: shed by the sample. And then the X ray detectors
Speaker 1: pick up X rays that would be emitted from underneath
Speaker 1: the specimen, and the beam scans the entirety of the
Speaker 1: specimen and the detector's data is used to construct the
Speaker 1: corresponding image. And that's how scanning electron microscopes work if
Speaker 1: you really want to dive more into that technology, because
Speaker 1: I realized again without visual aids it gets a little
Speaker 1: challenging to understand. There's a great article on how stuff
Speaker 1: works about how scanning electron microscopes work. Now, I'm gonna
Speaker 1: take a quick break, and when I come back, we're
Speaker 1: gonna look at some of the other cool technology used
Speaker 1: in forensic science. Now, in the last episode, I talked
Speaker 1: about ballistics and measuring stuff like bullet holes to determine
Speaker 1: the angle and direction of firearm was pointed before firing.
Speaker 1: And in the old days you do stuff like tape
Speaker 1: measures to figure all that out, you know, take physical measurements,
Speaker 1: but today you typically would use laser scanners, they can
Speaker 1: give you much more precise information. A laser scanner depends
Speaker 1: largely on the time of flight method. That's pretty much
Speaker 1: similar to sonar and radar or speed guns that that
Speaker 1: police use to detect the speed of a vehicle. The
Speaker 1: whole idea is what what amount of time does it
Speaker 1: take for a laser beam to travel from in the
Speaker 1: mirror to a sensor. Right, So by knowing the amount
Speaker 1: of time between when a pulse of lasers left a
Speaker 1: laser and when they were picked up by a sensor,
Speaker 1: you can know the distance it traveled. Because it's traveling
Speaker 1: at the speed of light. That's a constant. You can
Speaker 1: use that constant and then work backwards and determine how
Speaker 1: far did this laser beam travel. With laser scanners, you're
Speaker 1: talking about a detector built into the scanner itself, right,
Speaker 1: So they go. You've got an a mitter and a
Speaker 1: scanner and they're next to each other, and then you
Speaker 1: take half the distance that you calculate. Because the beam
Speaker 1: travels out, it hits an object, it travels back and
Speaker 1: gets picked up by the sensor, So that means the
Speaker 1: laser has traveled twice the distance between the point of
Speaker 1: the laser and the the point of contact. So you
Speaker 1: just take half of that that will tell you the distance. Right.
Speaker 1: So you use these laser scanners uh the time of
Speaker 1: flight scanners, and you move them in a grid fashion
Speaker 1: to capture all points of a scanned specimen, and then
Speaker 1: you get this this collection of data points that tells
Speaker 1: you how far away the various parts of a specimen
Speaker 1: were compared to the origin spot of the laser scanner.
Speaker 1: That would allow you to then plot that information in
Speaker 1: a computer and get a real good read on the
Speaker 1: specifics of whatever it was you were scanning. At three
Speaker 1: D dash forensic dot com, there's a description of this
Speaker 1: technology used to investigate a shooting crime to have then Vallejo, California.
Speaker 1: This one took place in there was a couple who
Speaker 1: were in a car that was outside of a home
Speaker 1: in California. An argument broke out, presumably between the couple
Speaker 1: and maybe with someone else as well who was outside
Speaker 1: the car on a porch in front of the house.
Speaker 1: That person on that porch fired an a K forty
Speaker 1: seven at the vehicle. One of the bullets struck and
Speaker 1: killed the driver of that vehicle, but the person who
Speaker 1: shot the a K forty seven later claimed that the
Speaker 1: passenger of this car had a gun and the passenger
Speaker 1: was threatening the person who was standing on the porch.
Speaker 1: So in California, there is something called the provocative act doctrine,
Speaker 1: which states that if someone incites a killing, if they
Speaker 1: escalate a situation and then a killing occurs because of
Speaker 1: that escalator, that person can be charged with murder. So
Speaker 1: the passenger in this car could be charged with the
Speaker 1: murder of the driver of that car because of this
Speaker 1: provocative act. Even though the passenger in the car wasn't
Speaker 1: the one who fired the gun, the argument would be
Speaker 1: because of the passenger's actions, the driver died, so the
Speaker 1: person charged is not the one who actually did the killing,
Speaker 1: but incited the killing to happen. So the prosecution is
Speaker 1: arguing the passengers actions lead to the death of this driver.
Speaker 1: And at the heart of the issue was whether the
Speaker 1: passenger actually did possess a gun and either threatened or
Speaker 1: perhaps even fired it at the person who was on
Speaker 1: the porch. The shooter who stood on that porch fired
Speaker 1: an a K forty seven in full auto mode, which
Speaker 1: means you just hold down the trigger and it will
Speaker 1: keep firing until you let go of the trigger, You're
Speaker 1: out of bullets. Investigators were brought in to answer quite is,
Speaker 1: like where was the car when it was struck by
Speaker 1: the two bullets? What is the line of sight from
Speaker 1: the porch of the house to the position of the car.
Speaker 1: If you assume the height of the person on the
Speaker 1: porches about five ft eight inches, that was the height
Speaker 1: of the shooter. What is the line of sight from
Speaker 1: the front passenger position to the porch, Because if the
Speaker 1: person in the passenger seat was actually threatening the person
Speaker 1: on the porch, they would have to be able to
Speaker 1: see that person. Was the vehicle in motion? If so,
Speaker 1: how fast was it going? And could the investigators determine
Speaker 1: the order of the two bullets that struck the car?
Speaker 1: Which one was first? The three D laser scan that
Speaker 1: the investigators used, uh, they made one of the bullet holes,
Speaker 1: they did of the car, the porch. They actually scanned
Speaker 1: the whole area, but they were looking at the bullet
Speaker 1: holes first, and that indicated that the two bullets that
Speaker 1: were both shot from the same angle, which indicated that
Speaker 1: the shooters stood in the same spot while firing the shots.
Speaker 1: But there were there was a distance between bullet hole
Speaker 1: number one and bullet hole number two, and that distance
Speaker 1: would mean that the car must have moved two point
Speaker 1: seven feet between those two shots. And the reason they
Speaker 1: realized that the car was the one that moved and
Speaker 1: not the person was because the a K forty seven
Speaker 1: was fired in full auto mode. The time between two
Speaker 1: shots from a cold start would be about one tenth
Speaker 1: of a second, which means the car must have moved
Speaker 1: to get two point seven feet further in one tenth
Speaker 1: of a second. That's way too fast for a person
Speaker 1: to have moved and been able to fire this gun,
Speaker 1: and it would mean that the car was moving at
Speaker 1: around a little less than twenty miles per hour. The
Speaker 1: investigators ended up conducting thorough laser scans not just in
Speaker 1: the vehicle, but the whole area where the crime occurred,
Speaker 1: and at the heart of the issue was conflicting testimony.
Speaker 1: Did the passenger have a gun? Was the passenger threatening
Speaker 1: or actively shooting the person on the porch? And based
Speaker 1: on the scans and simulations, the jury found the evidence
Speaker 1: did not support the shooters claim that the passenger was
Speaker 1: threatening the shooter with a gun, and so the charges
Speaker 1: of murder against the passenger were dismissed. So that's kind
Speaker 1: of an interesting way of using laser scanners. It's a
Speaker 1: pretty fascinating discussion. And again, if you go to that
Speaker 1: website three D dash forensic dot com, you can find
Speaker 1: the whole case study written up and in greater detail
Speaker 1: and learn more about it. So let's say let's change
Speaker 1: gears a little bit. Let's say you go to a
Speaker 1: crime scene and there's broken glass everywhere, and the cops
Speaker 1: have a suspect and custody, and a close examination of
Speaker 1: the suspect's clothing revealed that there were some glass particles
Speaker 1: that were attached to that clothing. They were they were
Speaker 1: just stuck on there. But the particles are really small,
Speaker 1: and it's not obvious that they come from the crime scene.
Speaker 1: They might be unrelated. So if you've got really small
Speaker 1: glass particles, they're so small that you can't just you know,
Speaker 1: piece them together, how can you determine whether or not
Speaker 1: they came from the crime scene. Well, you could call
Speaker 1: in the laser ablation inductively coupled plasma mass spectrometry device.
Speaker 1: It's also known as the l A I C p MS.
Speaker 1: One of those cases where the acronym is almost as
Speaker 1: clunky as the full name. It sounds like something out
Speaker 1: of Ghostbusters, doesn't it. But this is a Once you
Speaker 1: break it down into its component parts, it's a lot
Speaker 1: easier to understand because when you hear laser ablation inductively
Speaker 1: coupled plasma mass spectrometry, that seems like it would be insane,
Speaker 1: but it actually makes a lot more sense when you
Speaker 1: break it down. So first, let's talk about laser ablation.
Speaker 1: This is where you use a laser beam that is
Speaker 1: of a particular strength so that when you move it
Speaker 1: across a sample surface, it generates fine particles. Through laser ablation, essentially,
Speaker 1: you're shaving off particles from the sample. You gather these
Speaker 1: particles and they go into a chamber where an inductively
Speaker 1: coupled plasma instrument otherwise known as a plasma torch ionizes
Speaker 1: the particles. Once again, you uh impart a lot of
Speaker 1: energy to the particles, so it ends up ionizing them.
Speaker 1: It sheds electrons, it becomes charged, and then you put
Speaker 1: it through a spectrometer. The spectrometer separates the ions using filters,
Speaker 1: which aren't physical filters. It's not like a mesh or something.
Speaker 1: There in the form of first an electric field and
Speaker 1: then a magnetic field, and this forces the ions to
Speaker 1: fan out into a spectrum, and the ions will all
Speaker 1: fan out based upon physical uh features of those ions,
Speaker 1: So all like ions will end up in one part
Speaker 1: of the spectrum and unlike ions will be in a
Speaker 1: different part of the spectrum. So by looking at the
Speaker 1: whole spread of the spectrum, you can say what that
Speaker 1: substance was made out of. A detector will count up
Speaker 1: the ions and the various parts of the spectrum, and
Speaker 1: a computer program analyzes the results to tell you what
Speaker 1: it was that you zapped. And by analyzing a sample
Speaker 1: from a crime scene and then comparing those results to
Speaker 1: samples collected from a suspect, you can see if the
Speaker 1: glass was made out of the same stuff, and if
Speaker 1: it is, that's a clue that your suspect is someone
Speaker 1: to look at very carefully, as that match suggests that
Speaker 1: they must have come in contact with the crime scene.
Speaker 1: Now it's not it's not like smoking gun evidence, but
Speaker 1: it certainly suggests if there's a match, that they were
Speaker 1: involved in some way. Uh. If there's not a match,
Speaker 1: then you could say, well, according to our results the glass, Yes,
Speaker 1: you found glass on this person's clothing, but it doesn't
Speaker 1: match the glass that was found at the crime scene,
Speaker 1: so we can't say for certain that there was any
Speaker 1: connection there. That actually suggests there's not a connection. Then
Speaker 1: we can move on to stuff like document examination. This
Speaker 1: is where you're looking for, uh, any evidence that was
Speaker 1: left behind in kind of writing form, whether it was
Speaker 1: you know, handwriting or typing or printers whatever that maybe.
Speaker 1: And this can be used in all sorts of crimes,
Speaker 1: not just the kind of violent crimes I've sort of
Speaker 1: talked about before, but all certainly like corporate crimes, you know,
Speaker 1: that kind of stuff. So there's a lot of different
Speaker 1: ways of doing this. One way is to look for
Speaker 1: indented writing, you know, the idea that there's traces of
Speaker 1: someone having written something. It's not necessarily on a piece
Speaker 1: of paper. They're looking at maybe a piece of paper
Speaker 1: that was underneath the one that was being written on.
Speaker 1: Typically you would want to use something like oblique light
Speaker 1: and photography first. In other words, you're hitting the surface
Speaker 1: of the material that you suspect has indentations from previous
Speaker 1: writing with light from different angles in order to try
Speaker 1: and illuminate those indentations, and then you take pictures of it.
Speaker 1: But there's also a device called an electrostatic detection apparatus
Speaker 1: or E s d A that you can use. And
Speaker 1: you know, when you write on a top sheet of paper.
Speaker 1: Let's say you've got a pad of paper and you're
Speaker 1: writing on that top sheet, you might see that you've
Speaker 1: got indentations on the lower sheets and uh, and you
Speaker 1: would use a pencil to shade out those indentations to
Speaker 1: read writing. You see that in a lot of detective shows,
Speaker 1: right a detective sees a pad of paper next to
Speaker 1: a phone, picks up the pad of paper, grabs a pencil,
Speaker 1: shades the pencil across the pad of paper, and spells
Speaker 1: how the message like see pick up bag at third
Speaker 1: and Broad Street or something like that. And you're like, oh, okay,
Speaker 1: well voila. E s d A takes a slightly more
Speaker 1: electrifying approach to this concept. So an E s d
Speaker 1: A device generates an electro static field, and think of
Speaker 1: it like, you know, uh, static electricity, that idea of
Speaker 1: building up this charge. It imparts this electrostatic charge to
Speaker 1: a document that could have indentations on it. So these
Speaker 1: machines have a platform made out of bronze plate. You
Speaker 1: put the piece of paper you're gonna scan on top
Speaker 1: of that bronze plate on top of the piece of paper,
Speaker 1: you put a thin layer of film on there, and
Speaker 1: then you pass a highly charged wire called a corona
Speaker 1: over the paper. And it's this highly charged wire that
Speaker 1: imparts an electrostatic charge to the paper underneath. The indented
Speaker 1: parts of the paper received the largest amount of that
Speaker 1: electro static charge. Then once that's over, they can expose
Speaker 1: the film covered paper to toner, and the toner also
Speaker 1: has an electrostatic charge, but it's opposite to the charge
Speaker 1: that the corona gave the paper, and opposite charges a
Speaker 1: tract So the indented spots with the greatest amount of
Speaker 1: charge attract the toner. Then you can see where the
Speaker 1: invitations were. You can see them more clearly. You might
Speaker 1: be able to read stuff. It's really not that different
Speaker 1: from the way a photocopier works, if you remember my
Speaker 1: episodes about that. So I thought that was a pretty
Speaker 1: cool technology. Sometimes, however, you're not just looking for evidence
Speaker 1: that someone has actually written something on a piece of paper.
Speaker 1: You might want to determine if a document has been altered.
Speaker 1: For example, let's say someone's signed a contract and then
Speaker 1: later on they come to a court and they say
Speaker 1: the contract I signed is different from the one that
Speaker 1: they claim I signed. They must have changed it after
Speaker 1: I signed it. They might want to use something like
Speaker 1: a video spectral comparator device what the heck also called
Speaker 1: a VSC. So this is an imaging device. It combines
Speaker 1: multiple cameras, multiple sensors, and different lights to examine a
Speaker 1: document and the entire spectrum of light, including ultra violet
Speaker 1: and infrared that's beyond the visit spectrum, right We humans
Speaker 1: can't see that without technological aid, so a computer is
Speaker 1: able to render the results in shades we can see.
Speaker 1: So you've got these cameras that can pick up in
Speaker 1: these different frequencies, You've got lights in these different frequencies,
Speaker 1: and sensors in these different frequencies, and through all this
Speaker 1: you can analyze the data coming back and a computer
Speaker 1: can present it in a way that we can actually see.
Speaker 1: And the analysis of color is really important as it
Speaker 1: can detect when two different but similar incs were used
Speaker 1: on a document. So to our eyes, we might look
Speaker 1: at the document and say, well, this was clearly all
Speaker 1: written at the same time. We can put it through
Speaker 1: a an analysis like this, where you're using different wavelengths
Speaker 1: of light to analyze the document, and by taking precise
Speaker 1: measurements of the light that's coming off that document that's
Speaker 1: being reflected back from that document, you could say, well, actually,
Speaker 1: it turns out there are two different inks that were
Speaker 1: used on this document, which indicates that there were as,
Speaker 1: there was a point where it stopped and started up,
Speaker 1: and it was printed on a different device, and uh
Speaker 1: so to casual glance, it might look like this was
Speaker 1: all done at once, but you could say, well, no,
Speaker 1: the analysis shows there's two different inks here. They look
Speaker 1: the same to our human eyes, but when we put
Speaker 1: it through the vs C, we can clearly see that
Speaker 1: there were two different types of ink. So it's really
Speaker 1: helpful if you want to see if in fact the
Speaker 1: document has been changed, if something has been erased or replaced.
Speaker 1: Very interesting technology. Well, I've got some more that I
Speaker 1: want to talk about in the great world of forensic tech.
Speaker 1: But before I get to that, let's take another quick
Speaker 1: break to thank our sponsors. I just talked a bit
Speaker 1: about devices that use cameras. Might as well stick with
Speaker 1: cameras because photography is a really important part of forensic science.
Speaker 1: Let's say there's a case where a forensic nurse, and
Speaker 1: there are such things. A forensic nurse is called in
Speaker 1: to treat someone who appears to be the victim of
Speaker 1: a physical attack. This person might not be communicative, and
Speaker 1: this can be a matter of life and death. And
Speaker 1: sometimes evidence of physical harm is hard to see, particularly
Speaker 1: if that harm happened just a short time earlier. So uh,
Speaker 1: for example, there might not be evidence of bruising that
Speaker 1: it's that's visibly. Uh, they're right, but there may very
Speaker 1: well be damaged that will lead to that. So there
Speaker 1: are cameras that make use of a technology called alternative
Speaker 1: light source photography that can reveal evidence of physical harms
Speaker 1: such as bruising, before they become visible, and it allows
Speaker 1: medical staff to treat a person quickly, and sometimes that
Speaker 1: can be the difference between saving someone and losing them. Now,
Speaker 1: it's called alternative light source photography because those cameras may
Speaker 1: use something like infrared light or ultra violet light, or
Speaker 1: they might even use visible light, but it's in a
Speaker 1: very particular wavelength. For example, I saw one version of
Speaker 1: such a camera that uses blue light to illuminate a
Speaker 1: person's skin and then has a special orange filter to
Speaker 1: try and pick up any evidence of physical harm that
Speaker 1: might not be visible under normal lighting conditions, which I
Speaker 1: thought was really interesting. They're also high speed cameras that
Speaker 1: are frequently used to get a better understanding of ballistics evidence.
Speaker 1: High speed cameras can take images at incredible speeds, as
Speaker 1: the name suggests, and typically that requires a lot of light.
Speaker 1: You don't really use high speed cameras and low light conditions,
Speaker 1: and that's because cameras work by focusing light coming through
Speaker 1: a lens through an opening called the aperture, which can
Speaker 1: open or shrink. If you open, you allow more light
Speaker 1: to come through. If you shrink, you allow less light
Speaker 1: to come through. And you have a shutter. The shutter
Speaker 1: is a device that opens and closes and allows the
Speaker 1: light to either pass through and expose an image on film,
Speaker 1: or it hits a digital sensor, right for for digital photography.
Speaker 1: With high speed photography, this has to happen really really fast.
Speaker 1: Right You're you're creating images at an incredible rate, So
Speaker 1: the shutter has to be able to open and close
Speaker 1: super super fast, and that means you have to have
Speaker 1: a very well lit scene because the shutter is just
Speaker 1: allowing light through or not allowing light through, and if
Speaker 1: it's moving super super fast, not a whole lot of
Speaker 1: light gets through on each time it opens, So you
Speaker 1: want to have a very bright scene in order to
Speaker 1: be able to see anything. Otherwise the video or film
Speaker 1: that you take is going to be very very dark.
Speaker 1: There's also a thing called a gunshot residue scanning electron
Speaker 1: microscope as another detection tool that can help look for
Speaker 1: a gunshot residue. No big surprise based on the name.
Speaker 1: It's actually a combination of hardware in software, and typically
Speaker 1: these things look like big desktop computers, you know, with
Speaker 1: a couple of monitors, big tower. There might be some
Speaker 1: specialized peripherals attached to it, but you know, if you
Speaker 1: looked at a casual glance, you might just say, oh,
Speaker 1: that's just a desktop computer. The microscope works like the
Speaker 1: scanning electron microscopes i mentioned earlier, looking for any suspicious
Speaker 1: particles that could be the residue from a firearm discharging,
Speaker 1: and then the system uses spectroscopy to identify what those
Speaker 1: particles are. So both the technologies are referred to earlier
Speaker 1: in this episode would be combined in this kind of
Speaker 1: approach to first look at very closely a material that
Speaker 1: you suspect might have gunshot residue on it, and then
Speaker 1: through spectroscopy, do this analysis to determine are there, in
Speaker 1: fact any particles there that would indicate gunshot residue. On
Speaker 1: TV and movies, we often see investigators using technology like
Speaker 1: three D facial reconstruction technology UH. The technique uses algorithms
Speaker 1: to determine what someone might have looked like based upon
Speaker 1: typically remains. It's pretty grim stuff, so you find remains
Speaker 1: at a scene, maybe you find skeletal remains, and you
Speaker 1: wonder what did the person look like in life, and
Speaker 1: you're trying to reconstruct that that That technology really does exist,
Speaker 1: though it has shown to be variable in its reliability
Speaker 1: depending upon the actual implementation. It doesn't always work perfectly,
Speaker 1: and it depends heavily upon the software packages that you use. Typically,
Speaker 1: you would use software UH to analyze a scan of
Speaker 1: the remains, So you're using scanners to completely get a
Speaker 1: very detailed representation of those remains, and the software would
Speaker 1: then go over that information, and you might also have
Speaker 1: to include other information you might have about the person,
Speaker 1: like if you know anything about their age, their gender, UH,
Speaker 1: their ancestry. All of that could be taken into account
Speaker 1: by the software package while it's trying to build out
Speaker 1: what the person might have looked like, uh, in life.
Speaker 1: And then you might feed the software some images of say,
Speaker 1: missing persons. Let's say that you've got a file of
Speaker 1: people who have gone missing. You might feed those images
Speaker 1: through to see if the computer system can find any
Speaker 1: matches between the reconstruction that's created and any actual humans
Speaker 1: that you have pictures of, and if there are any
Speaker 1: matches that would allow you to help narrow down your investigation. Potentially,
Speaker 1: it doesn't. Again, it's not necessarily a hit, but it
Speaker 1: could mean that you are you've got a lead to follow.
Speaker 1: As I said, the reliability of the software depends upon
Speaker 1: the actual software package used, so it's it's not infallible.
Speaker 1: We also see a lot of news about DNA evidence,
Speaker 1: which is really important stuff. Let's say you recover some
Speaker 1: DNA evidence at a crime scene that doesn't match any
Speaker 1: of the known people to have been there, right, so
Speaker 1: what or it's a violent crime or not. You find
Speaker 1: some DNA evidence, you've eliminated the people who typically are
Speaker 1: at that place, and you want to know who the
Speaker 1: heck does this DNA belong to, It could belong to
Speaker 1: the perpetrator of a crime. So you take the DNA
Speaker 1: in for analysis. You first replicate that DNA millions of
Speaker 1: times for the purposes of testing, so that you have
Speaker 1: enough of it to work with, and then you analyze it.
Speaker 1: And scientists can use phenotyping to identify genetic markers and
Speaker 1: DNA variants and based upon that information make predictions about
Speaker 1: the appearance of the person who that DNA belongs to.
Speaker 1: These predictions are very general, so they're also based off probabilities.
Speaker 1: Nothing is totally certain. You can't just scan the DNA
Speaker 1: and say, ah, I know exactly what this person looks like,
Speaker 1: but you can get some general predictions. There's a couple
Speaker 1: of different systems that can do this. There's one in particular,
Speaker 1: the hi risplex system that I read about. According to
Speaker 1: what I read, it can predict blonde hair. Uh. If
Speaker 1: it's got the markers for blonde hair, it can predict
Speaker 1: whether the person has blonde hair about sixty nine five
Speaker 1: percent at the time. Now, blonde hair that's carried by
Speaker 1: a recessive gene, it's not really surprising that the success
Speaker 1: rate is below. Brown hair gets a much higher hit
Speaker 1: rate at seventy eight point five percent, red hair even
Speaker 1: higher at eight percent, and black hair gets the highest
Speaker 1: at eighty seven point five. The system can also use
Speaker 1: the same sort of methodology to predict what color eyes
Speaker 1: the person probably has, and so then if that's all
Speaker 1: you have to go on, if there are no why witnesses,
Speaker 1: but you have some DNA evidence, you could say, well,
Speaker 1: based upon our analysis, there's the x amount of chance
Speaker 1: the person has brown hair and blue eyes, and so
Speaker 1: that at least gives you some parameters you can start
Speaker 1: to look for when you're doing your investigation, although again
Speaker 1: you have to remember these are all based on probabilities,
Speaker 1: not certainties. And this next one goes out to all
Speaker 1: you gamers out there. We live in an age where
Speaker 1: there are numerous ways to store electronic data. You might
Speaker 1: have a computer, a smartphone, a tablet, USB drives, hard drives,
Speaker 1: optical discs. If you're clinging to the past, you might
Speaker 1: use cloud storage. But one device that sometimes can be
Speaker 1: used to store incriminating information is the good old game
Speaker 1: console like the Xbox, and a moded Xbox can be
Speaker 1: used to store all sorts of information of questionable legality,
Speaker 1: not to mention stuff that's just outright illegal, and uh
Speaker 1: mods can exploit known vulnerabilities in the Xbox. You don't
Speaker 1: necessarily have to crack the Xbox open and do some
Speaker 1: soldering to change things. There was one example that was
Speaker 1: cited in a paper titled x f T, a Forensic
Speaker 1: Analysis Tool for the Microsoft Xbox Game Console. It was
Speaker 1: written by a guy named David Collins, and he pointed
Speaker 1: out that there was an Xbox game Double O seven
Speaker 1: Agent under Fire that had a vulnerability. An Xbox owner
Speaker 1: could visit a link and download an exploit that was
Speaker 1: created by a hacker. The exploit used the buffer overrun
Speaker 1: vulnerability in that game for the saving process. So on
Speaker 1: the Xbox, it would look like it was a valid
Speaker 1: saved game. That's what the file would look like. It's like, oh, well,
Speaker 1: that's just that's just a save game file, But in
Speaker 1: reality it would be an operating environment. The Xbox owner
Speaker 1: could use that operating environment to browse files using the
Speaker 1: FTP protocol and download files to the Xbox and the
Speaker 1: guys of this save file, so on casual glance, it
Speaker 1: wouldn't look like anything was hinky. Now, the Xbox used
Speaker 1: a file system called f a t X that is
Speaker 1: not readable by most forensic software. So let's say you're
Speaker 1: on an investigation and you want to check the Xbox
Speaker 1: for any illegal information. It might not be readily apparent
Speaker 1: that such information is on that Xbox if you don't
Speaker 1: know where to look, and you can't easily scan it
Speaker 1: with most forensic software. So digital forensics experts developed a
Speaker 1: tool called the x f T, which is a command
Speaker 1: line utility. It behaves like a Linux shell and allows
Speaker 1: an investigator to image the file system of an Xbox,
Speaker 1: which then would allow an analyst to browse the contents
Speaker 1: on the game console in the search for illegal material.
Speaker 1: And it can record a browse session so that prosecutors
Speaker 1: could present that to jurors in a trial to show
Speaker 1: exactly where a criminal hid data on the game system. Now,
Speaker 1: one forensic tool I think is really neat is actually
Speaker 1: not high tech at all. It's actually pretty low tech.
Speaker 1: But that's kind of why I like it. It's so elegant,
Speaker 1: and it's the use of magnetic fingerprint powder and magnetic wands.
Speaker 1: Sounds very hairy potter ish, but it's not the powder.
Speaker 1: The magnetic powder. It's dark. It can be used as
Speaker 1: you know dark powder, black powder that you would typically
Speaker 1: use when dusting for prints, but this particular powder contains
Speaker 1: iron filings in it, which means it's attracted to magnets.
Speaker 1: So when you want to dust a surface for prints,
Speaker 1: you take out the magnetic wand. Now this is essentially
Speaker 1: a plastic cylinder, and there's a cap on one end
Speaker 1: of this plastic cylinder. It's got an end on a
Speaker 1: capped end. Inside the cylinder is a magnet that's on
Speaker 1: the end of a plunger. So if you push the
Speaker 1: plunger all the way down, the magnet is pressed up
Speaker 1: against the back end of that cap, the inside of
Speaker 1: the cap. Then you can use the wand to pick
Speaker 1: up the magnetic powder and it's going to clump to
Speaker 1: the end of the wand you would then gently move
Speaker 1: the wand across the surface that you are dusting for prints,
Speaker 1: and you would use it like it's a brush, except
Speaker 1: instead of it being the bristles of a brush, it's
Speaker 1: actually the magnetic powder itself. And you're not letting the
Speaker 1: wand contact the paper, it's just the powder. So as
Speaker 1: you do this, some of the magnetic powder comes loose,
Speaker 1: and if their fingerprints on the surface, the powder will
Speaker 1: reveal the presence of those fingerprints. Once you're done brushing
Speaker 1: the surface, you can then move the wand back over
Speaker 1: to the container of magnetic powder. You position the wand
Speaker 1: over the contain inner so that you're being nice and
Speaker 1: careful and neat, and then you pull the plunger back
Speaker 1: up the length of the cylinder. This moves the magnet
Speaker 1: away from that capped end, and the magnetic powder will
Speaker 1: just fall freely down into the container because there's no
Speaker 1: longer that they're no longer close enough to the magnetic
Speaker 1: field to be attracted to it anymore. One thing that
Speaker 1: you do have to take into account if you're using
Speaker 1: this stuff is it is more abrasive than normal black powder,
Speaker 1: so brushing has to be very gentle. As for future
Speaker 1: technologies and forensics, we might see investigators look at stuff
Speaker 1: like the microbiomes we carry with us, those those or
Speaker 1: those kind of cultures of micro organisms that are unique
Speaker 1: to us. No two people have the same microbiomes, although
Speaker 1: sexual contact can intermingle the microbiomes of one person and another.
Speaker 1: In fact, an investigation could reveal that. So say it's
Speaker 1: a it's a case where someone is coming forward and
Speaker 1: they have an accusation and in volves sexual assault, then
Speaker 1: investigation of the microbiome might be one of the ways
Speaker 1: you could confirm that uh it. So being able to
Speaker 1: identify and classify microbioms could become a really important investigative
Speaker 1: tool in cases where you may not have a good
Speaker 1: DNA sample to work with. UH. For that to happen,
Speaker 1: that scientists have to prove that it's a reliable way
Speaker 1: of identifying a person. UH that they have to show
Speaker 1: that it is in fact something that you could base
Speaker 1: a legal case on and it's so they have to
Speaker 1: show that it's it's a verifiable and reliable technology. Another
Speaker 1: line of investigation might focus on pollen particles that can
Speaker 1: indicate specific travel patterns people have taken based upon the
Speaker 1: pollen they've come in contact with and they have on
Speaker 1: their clothes or skin. The study of pollen is called
Speaker 1: palein ology p A L Y N O L O
Speaker 1: g Y. It's pretty hefty stuff because there are a
Speaker 1: hun ords of thousands of species of flowering plants out there,
Speaker 1: so it is not easy to identify pollen UH necessarily,
Speaker 1: but it could be a promising addition to the forensic
Speaker 1: investigators growing collection of tools and strategies. And there's other
Speaker 1: stuff that didn't talk about. I mean, there's stuff where
Speaker 1: you could look at the computer system on a car
Speaker 1: to look for uh, indications of things that you might
Speaker 1: suspect based upon a crime that might have been committed
Speaker 1: by someone driving. There's a lot of different avenues of
Speaker 1: investigation out there, and honestly, I could do a full
Speaker 1: podcast series about these, but I thought it was interesting
Speaker 1: to kind of give this this look into what's being
Speaker 1: used today and the technologies that might be used tomorrow.
Speaker 1: Uh So thanks a lot Hakim who asked us to
Speaker 1: look into this, I greatly appreciate it. If you have
Speaker 1: a suggestion for a future episodes tech stuff, why not,
Speaker 1: right and let me know what that is. The addresses
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Speaker 1: at both of those is tech stuff. H s W.
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