Name: 犯罪現場のプロが解説、血痕から分かる犯人の足跡 | WIRED.jp
Uploaded: 2022-01-13T18:00:06.000Z
Duration: 17 min 8 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Hi, I'm Matthew steiner Matt is a certified senior crime scene analyst.

He's explained crime scene forensics in technique critique.

So, that's a really interesting yet very illegal way to get DNA from somebody today.

I'm gonna show you how to analyze various bloodstain patterns in this episode.

We'll learn the techniques forensics experts used to investigate bloodstain patterns ranging from easy to difficult.

So normally when we go to a crime scene, it's not set up like this unless we have some sort of dexter X crime scene where the killer really planned it out.

For us at crime scenes, when we investigate them, safety is number one, we want to protect ourselves.

I think the various blood borne pathogens that we're dealing with.

And secondly, we don't want to contaminate the crime scene so we don't want the hairs and fibers on ourselves.

The DNA that shedding off us falling onto our evidence at a crime scene.

If we're gonna be handling evidence and then we'd want to wear eye protection if there's like a splash hazard with blood that hasn't been dried.

So our tyveK suit covers most of our body, including our feet because we wanna be introducing our shoe wear impressions into a crime scene or destroying evidence that's there.

So, normally I'd be wearing a mask, but I don't think it's really good look for talking on camera.

Next we're gonna talk about the three main categories of bloodstains that we can encounter at a crime scene.

Today, we're gonna be using defib renate id sheep's blood.

We have taken the fiber and out of this blood fiber and is a protein that's in our plasma that causes our blood to clot.

So, if we use regular whole blood that had the fiber in it, we'd have a clotted mess inside this bottle bloodstain pattern, analysts correlate the appearance of these blood stain patterns at a crime scene to a mechanism by which they were created.

It isn't like the way tv presents it where a crime scene investigator walks into a scene and can tell you every single action that happened inside that crime scene from beginning to end, analyst can correlate the static bloodstains at a crime scene with dynamic forces that create them.

So, we look at is specific stain patterns and we could figure out how they possibly were created.

And then with that we could show a small window of time.

Not the whole crime, but that this type of force could have created this sort of pattern.

So, passive patterns are patterns that are created without any sort of outside external forces other than gravity or contact.

So, we're going to first start off with dropping blood at 90° to see what we get.

So, I'm going to take pipette and a small amount of blood and hold it directly above and drop it.

So, when our sphere of blood strikes a surface at 90 degrees, we have a very even round circle at a crime scene but also what affects the way our bloodstain looks is the surface itself.

We have plexiglass and we notice that the edge characteristics of our blood stains are very even now that we observe the way that blood acts on a smooth surface.

Let's try tile which has a little bit of texture to it.

One drop of blood straight down onto a different surface.

Now you can see a little bit of scalloping around the edges there.

So the scalloping is just the different ways that we describe the edge characteristics of blood stains.

So it could be smooth uniform, it could be scalloped or it could be spiny.

So now we change the surface to a rougher surface would so we can see a vast difference from where we started where we have a smooth edge characteristics.

Now we have this spiny er pattern because that blood drop is being disrupted by the surface itself.

And we can also see we have some satellite stains.

Satellite stains are the stains that come off a parent stains.

So this main stain here's my parents stain in this case because the disruption they are being forced out from the center of it.

We also see satellite spatter when blood is being dripped into blood.

Typically at a crime scene, especially with stabbings.

It could be that the suspect accidentally cuts themselves and they're moving around the crime scene and fleeing the crime scene.

And they could leave blood trails that we could follow.

A transfer pattern is a passive pattern where we have a bloody surface coming in contact with another surface.

And sometimes we can actually figure out what made that transfer, whether it was a hand or a weapon or someone's clothing.

I mean, that's the best type of innocent we could have at a crime scene.

So we have the victim's blood and we have the suspects impression.

There's very few explanations of how that happens.

So we're gonna start off with a shoe wear impressions in blood.

So this could be our victim walking through blood creating patterns in our crime scene, or this could be the suspect's shoe wear impressions were going to coat the bottom of the shoe and we're gonna transfer the pattern at the bottom of the shoe to our clean surface.

I have my shoe wear that's completely coated in blood and then inside that crime scene, we have a transfer of that pattern and we'll notice is that that pattern gets lighter and lighter as we move a lot.

We could find later on with chemicals like Luminol and bluestar.

So we could see a continuation of that pattern as someone walks away from a crime scene.

Sometimes we see transfer patterns in textiles.

So next we're gonna take some blood saturated portion of our genes with it and we're gonna transfer that onto our surface.

So sometimes in real crime scenes these get misinterpreted as the lines of minutia in your fingerprints or a palm print we would see is that unlike fingerprints, are just straight lines.

Either way, we would document this and collected and sent to the lab and then under magnification, analyze it.

So next we're gonna discuss how movement could affect these transfer stain patterns.

So I'm going to take some blood and put it onto my hand and then move that across the surface.

So if I touched the surface and then move my hand, we see what's called feathering.

The effect of movement on blood, just like if I took a paintbrush and moved it across the wall in the beginning would be darker, but eventually it will get lighter.

So this feathering effect helps us interpret movement at a crime scene.

This could be found at a crime scene in many different ways.

One could be a suspect has blood on their hands and they move it across a clean surface.

And another very common way that we see these patterns at a crime scene or what's called drag marks.

We have a victim that is bleeding and either they're moving through the scene or someone's dragging them through the scene and we see the same effect that feathering going towards the body.

Next we're gonna cover flow patterns and that is the volume of blood being affected by gravity.

So we can see here is that gravity is pulling up on that blood and pulling it down on our surface at crime scenes.

This may be very valuable evidence when we observe our victim's injuries.

Person had an injury to their shoulder if they're standing or if their body is erect, that flow patterns should go straight down their arms.

But if they've been moved or this movement or that injury was caused when they're laying down, we'd see a different flow patterns.

So next we're going to discuss saturation and pooling patterns that we have at a crime scene saturation.

Pooling patterns could tell us that someone is bleeding in a certain part in the crime scene for a period of time.

You know, sometimes when we see bubbles at a scene, that could mean that we have a expiration pattern or a pattern that's coming from an airway.

But what this could tell me is that we had accumulation of blood there and that there has been no movement because if this happened and then we moved the shirt, we would see that the blood would move in that direction, typically will see this on mattresses or beds or bedding and then it would absorb a little more.

So now we're gonna have an accumulation of blood on a non porous surface and we'll see pooling.

So pooling and saturation, it's the same mechanism that we're looking at.

But pulling the blood is not being absorbed into the surface for pools of blood, what we'll see with actual whole blood that has fiber and in it they will dry a lot slower than it would in something that's absorbent.

But also we're going to see over a period of time is clotting inside that pool and then sometimes we'll see affect what's called serum separation.

So the edges of this will be clear where we see the plasma of the blood as it separates.

So now we're moving on to the spatter category of bloodstain pattern analysis with this category of bloodstains were looking at some sort of external force on an open source of blood.

So I'm gonna do is I'm gonna put a small amount of blood on her.

Would here, I'm gonna strike it with a hammer.

And what we should see is that impact spatter on the plexiglass in front of us, put on my goggles, I'm gonna put my hood up, give us a small amount of blood here.

So as you can see, not only do we have impact spatter on the plexiglass in front of us.