Hey, Mr. P here. In this video, we're going to talk specifically about types of evidence. So we've moved out of chapter one and all of the observations and being a good eyewitness and the limitations of eyewitness testimony.
And we're going to move kind of more into the actual crime scene investigation. So we're going to talk about types of evidence, the limits of different types of evidence, the benefits of different types of evidence, and then we'll move on into the next video. in which we will talk specifically about the crime scene investigation team, as well as what to do actually at the crime scene once you're there. So, let's jump in and get started.
In this specific chapter, again, in this particular video, we're going to talk or focus on the low-card principle of exchange. We're going to talk about what that is. We're going to identify four examples of trace evidence in this video. and we're going to describe the difference between direct and circumstantial evidence in this particular video as well. In the next video, we're going to focus on the bottom two objectives for this particular chapter, which is identify the types of professionals who may work at a crime scene and summarize the seven S's of investigating a crime scene.
Again, in this particular video, just because I don't want it to be too long, we're going to focus on the top three. Okay, so what is Locard's principle of exchange? Lockhart's principle of exchange is the principle that talks about when things touch each other, when people touch things, when fabrics touch other fabrics, when fibers touch other fibers, they transfer from one textile to another. And so we as individuals, because we have fibers, and because we have hairs, and because we have skin cells, and because we have a whole bunch of other...
fibers within the textiles or the clothing that we wear, leave behind traces of things that we touch, okay? Or we leave behind on things and on people that we touch. The things and people we touch have traces behind or leave traces behind on us. So we are walking around with things attached to us that we have transferred from the things we've touched.
And we've also transferred things that are from us to the things we've touched. These traces may or may not be visible, which means you sometimes can see them and sometimes you can't. For instance, pet hairs can be transferred from a pet to the clothing that you're wearing, or they can be transferred from the pet to the couch, or from the pet to the carpet, or from the pet to your car seat, right?
And those are visible. You often can tell where and where... where the dog has been and where the dog hasn't been just based on the ability of a dog to leave hairs on things that it touched.
That's just a common example of Locard's Principle of Exchange. Hairbrush. Hairbrush often contains human hairs.
Why? Because the hairbrush contacts the human head, because that's what a hairbrush is used for. You brush your hair with it.
And so hairs can actually be transferred from the individual to the hairbrush. That's another example of principle of exchange. Those fibers, those hairs are being transferred from the individual to the hairbrush and you can actually visibly inspect the hairbrush and see the transfer has happened. Another thing is a pet brush. Very similar to the human hairbrush but pet hair can be transferred to a pet hairbrush as well.
And then fingerprints. I know it's kind of hard to see on this image, but on the outside of this glass, you can actually see kind of the impressions as the fingers are contacting the glass. And as soon as the individual puts the glass down, those fingerprints would be transferred to the glass.
And those are obviously less visible, at least without closer inspection, than hairs and fibers and stuff like that. But all of them... are basically pieces of evidence, trace evidence, that are left behind as a result of contact between two things. Another perfect example of Locard's principle of exchange is human skin cells.
So this is a really close-up electron micrograph of the human skin, and you can kind of tell that they are flaky, or at least you have all of these little flakes on them. And so we are constantly shedding off or flaking off skin cells and those skin cells can be transferred to the things that we touch. Okay, there's skin cells all over your house, there's skin cells all over your clothes, there's skin cells in your car, right? You can't help it. You're constantly flaking those off and you're constantly leaving them behind all of the places that you've been.
Okay, that's just another example of Locard's Principle of Exchange. Another one in this case is soil has been transferred from an individual's shoe to a rug, right? So that is another example of Principle of Exchange because you are exchanging.
trace evidence in the form of soil, in this case, from a shoe to the carpet. But it even kind of goes beyond that. The principle of exchange happened first from the ground where the soil actually was to the bottom of the shoe. That is a transfer.
And then you have the transfer, the secondary transfer, from the shoe to the carpet. Then there could be kind of that third level of transfer if somebody else came along and walked over the top of these footprints and potentially would have transferred the soil from the carpet to the individual that walked over them a second time. And then you have over here blood drops.
Blood can be transferred on a variety of textiles. In this case, it's on fabric. But blood can be transferred to Kleenexes.
It can be transferred to sheets. It can be transferred to carpets. It can be transferred to clothing. That is trace evidence, blood, fluid in this case, being transferred from one individual to another. Another example of Locard's Principle of Exchange.
So what is evidence? Evidence is basically anything that doesn't belong or possibly does belong in a particular area, but helps lead investigators in the right direction. And so there are different types of evidence, which is really the purpose of this video. And so under the umbrella term of evidence, we have two kind of divisions within evidence. One half of the evidence is direct evidence.
The other half of evidence is circumstantial evidence. And I'm going to go through all of these different types and give you examples of them. But evidence can be either direct or circumstantial. Okay. If evidence is circumstantial, it can be physical or biological.
And again, I'm going to go through all of these, but I just kind of want you to visualize this flowchart. Evidence can be direct or circumstantial. If it is circumstantial, it can be physical or biological. Okay, and so what do these terms mean? Direct evidence is the evidence that is taken basically directly either from the crime scene or is directly a confession.
or is a recording, right, or is an eyewitness account. It's coming directly from an individual that was there, an individual that did it, right, in the case of a confession. It could be victim testimony, right?
It's direct evidence, and it comes directly from the crime scene, okay? So eyewitness accounts, recordings or videos of an event, okay? Videos don't lie.
Videos record exactly what they saw, and so if there is a crime committed on tape, on video, that is a direct or a piece of direct evidence. Confessions by suspect is direct evidence, right? It's directly coming from the individual, which is really powerful, right?
A confession is probably the ultimate form of evidence in any particular criminal case because they're telling you exactly what happened, right? So that's direct evidence. Circumstantial evidence is the evidence that is indirect. So we have, remember that flow chart, direct and circumstantial. So the direct evidence is direct, circumstantial evidence is indirect, and it might suggest, keyword, suggest something is true but doesn't prove it.
Direct evidence proves, circumstantial evidence doesn't prove. So that's really important too. How does direct evidence prove? Well, direct evidence in the form of video shows exactly who did it, what they did, when they did it, etc.
Circumstantial evidence is evidence, and it can be very powerful evidence in the case of potentially like DNA or in the case of a fingerprint. You know, those are really good pieces of information and really good pieces of evidence, but they don't necessarily prove that somebody did something, right? Eyewitness testimony, video recordings, audio recordings, confessions, those are all proof that somebody did something.
Circumstantial evidence, again, does not prove it. It might suggest it, but it doesn't prove it. So you need a lot more circumstantial evidence to help paint the picture than you would, let's say, if you had...
the testimony or the confession. So, circumstantial evidence. For example, finding a suspect's gun at the crime scene may link the suspect to the scene, but there is a problem, though, and what is that problem? The suspect might own the gun, but it is plausible and reasonable. to think that he could have given it or loaned it or let somebody borrow it, right?
And so it might link him to the crime scene, but it might not, in a lot of cases, prove that he did it simply because other people can use his gun or other people can use his car or other people could use his clothes or use his shoes, right? It's like you're seeing the problem with that. So there is a problem with circumstantial evidence, but it can be powerful. Especially when you get a lot of circumstantial evidence that helps kind of paint the entire scene. Class evidence.
Class evidence is a group of evidence that helps to narrow down people or a group of people or narrow down the list of suspects based on people within that class. What do I mean by that? Blood type is an example of class evidence because there are different classes of people within different blood types.
So you might have a positive blood type. Well, if there's a positive blood type left at the crime scene because the perpetrator cut themselves, that's going to rule out anybody that is type O. It's going to rule out anybody that's type AB. It's going to rule out anybody that's type B.
It might even rule out anybody that's type A negative. But it does rule in... all the people that are type A positive.
Does it prove guilt for one individual? No, because you could have a couple different suspects that all have type A positive blood. It doesn't prove one individual did it over another.
It just rules out other groups, or we call that other classes of people. Tire marks, another example of class evidence. It is plausible to think that multiple people are driving around on the same brand and make and size of tire.
It does help narrow down because not everybody has the same make and brand and size of tire, but it helps to narrow down and focus on a shorter list of suspects due to the fact that tire marks can be used as a piece of evidence. And then paint chips, another example of class evidence, because paint chips help to... narrow down the suspect pool because paint chips are different colors. There's different metallic flakes, right?
There are different chemical compositions, stuff like that. So you're a forensic scientist analyzing hair believed to belong to an unknown suspect. You determine the hair has not been dyed and is from a blonde person.
Which group of people can you rule out? Well, you can pretty much guess that you can rule out anybody that is not naturally blonde because your hair that you found at the crime scene is blonde. Does that make sense? So that is a form of class evidence because you can rule in a certain kind of narrowed list of individuals or a smaller class of individuals. You can narrow out other groups or class of individuals as well.
Individual evidence. One of the most important pieces of evidence is individual evidence, and this kind of evidence is unique because it can specifically identify one single individual. which obviously has value, right?
So what kinds of evidence do you think could the individual evidence include? Well, obviously DNA, because everybody's DNA is unique, right? So one thing that you need to think about is individual evidence equals unique evidence, right? If it's evidence that is unique to you as an individual, it is a form of individual evidence. If you're the only one that has this particular trait or this particular entity, it is a form of individual evidence.
Nobody shares the DNA that you share unless you're a twin, right? Nobody shares the DNA, so that is a form of individual evidence. If my DNA is found at a crime scene, it would link me and only me to the crime scene.
That is individual evidence. Fingerprints, another example of individual evidence, because fingerprints are, just like DNA, unique to the individual. If they find my fingerprints at the crime scene, it links me and only me to the crime scene.
That is a form of individual evidence. Really, really powerful. Okay, that's where I'm going to end the video.
If you have questions, bring them to class. See ya.