Forensics Expert Explains How to Analyze Bloodstain Patterns

There we go.

Hi, I'm Matthew Steiner.

[Woman] Matt is a certified Senior Crime Scene Analyst.

He's explained crime scene forensics

and technique critique.

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.

[Woman] In this episode,

we'll learn the techniques forensics experts use

to investigate bloodstain patterns

ranging from easy to difficult.

Normally when we go to a crime scene,

it's not set up like this unless we have

some sort of Dexter-esque crime scene

where the killer really planned it out.

Today we're doing it on set for safety purposes.

For us at crime scenes when we investigate them,

safety is number one.

We wanna protect ourselves.

There could be various bloodborne pathogens

that we're dealing with and then secondly,

we don't wanna contaminate the crime scene.

We don't want the hairs and fibers on our cells,

the DNA that's shedding off of us

falling onto our evidence.

At a crime scene, we'd wear multiple layers of gloves

if we're gonna be handling evidence

and then we'd wanna wear eye protection

if there's like a splash hazard

with blood that hasn't been dried.

Our Tyvek suit covers most of our body

including our feet because we don't wanna

be introducing our shoe wear impressions

into a crime scene or destroying evidence that's there.

Normally I'd be wearing a mask,

but I don't think that's a really good look

for talking on camera.

Next, we're gonna talk about the three main categories

of blood stains that we can encounter at a crime scene.

Today we're gonna be using defibrillated sheep's blood.

We have taken the fibrin out of this blood.

Fibrin is a protein that's in our plasma

that causes our blood to clot.

If we used regular whole blood

that had the fibrin in it,

we'd have a clotted mess inside this bottle.

Bloodstain pattern analysts correlate

the appearance of these bloodstain patterns

at a crime scene to a mechanism

by which they were created.

It isn't a crystal ball.

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.

Analysts 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 can figure out how they possibly were created

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

Not the whole crime, but this type of force

could have created this sort of pattern.

Passive patterns are patterns that are created

without any sort of outside external force

other than gravity or contact.

We're gonna first start off with dropping blood

at 90 degrees to see what we get.

I'm going to take pipet

and a small amount of blood

and hold it directly above and drop it.

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 bloodstain

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.

That's because of the surface texture.

The scalloping is just different ways

that we describe the edge characteristics of bloodstains

so it could be smooth, uniform, it could be scalloped,

or it could be spiny.

Now we change the surface to a rougher surface, wood.

We can see a vast difference from where we started

where we have smooth edge characteristics.

Now we have the spinier pattern

because that blood drop is being disrupted

by the surface itself.

And we could also see we have some satellite stains.

Satellite stains are stains that come off a parent stain,

so this main stain here is my parent stain.

In this case because of 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,

we wanna look for these drip patterns.

It could be that the suspect accidentally cuts themselves

and they're moving around a crime scene

and they're fleeing the crime scene

and they could leave blood trails that we could follow.

Next we're gonna be looking at contact transfer stains.

A transfer pattern is a passive pattern

where we have a bloody surface

coming in contact with another surface

and then sometimes we could actually figure out

what made that transfer whether it was a hand

or a weapon or someone's clothing.

That's the best type of evidence

that we could have at a crime scene.

We have the victim's blood

and we have the suspect's impression.

There's very few explanations of how that happens.

We're gonna start off with a shoe wear impression in blood.

This could be our victim walking through blood,

creating patterns in our crime scene,

or this could be the suspect's shoe wear impression.

We're gonna coat the bottom of the shoe

and we're gonna transfer the pattern

of 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 along.

What we don't see with our naked eye

we could find later on with chemicals

like luminol or BlueStar.

We could see a continuation of that pattern

as someone walks away from a crime scene.

Sometimes we see transfer patterns in textiles.

Next we're gonna take some blood,

saturate a portion of our jeans with it

and we're gonna transfer that onto our surface.

Sometimes in real crime scenes,

these get misinterpreted as the lines that move from

your fingerprints or palm print.

What we see is that unlike fingerprints,

they're just straight lines.

Either way, we would document this and collect it

and send it to the lab and then under magnification,

analyze it.

Next we're gonna discuss how movement

could affect these transfer stain patterns.

I'm gonna take some blood and put it on my hand

and then move that across the surface.

So if I touch this surface and then move my hand,

we see what's called feathering,

the effect of movement on blood

just like if I took a paint brush

and moved it across a wall.

In the beginning it would be darker,

but eventually it would get lighter.

This feathering affect helps us interpret

movement at a crime scene.

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

One could be our suspect has blood on her hands

and they move it across a clean surface

and another very common way that we see

these patterns at a crime scene

are what's called drag marks.

We have a victim that's bleeding

and either they're moving through the scene

or someone's dragging them through the scene

and we'd see the same effect,

that feathering going towards the body.

Next we're gonna cover flow patterns

and that is a volume of blood

being affected by gravity.

So what we can see here is that gravity

is pulling upon 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.

A person had an injury to their shoulder.

If they're standing or if their body is erect,

that flow pattern should go straight down their arm

but if they've been moved or there's movement

or that injury was caused when they were laying down,

we'd see a different flow pattern.

Next we're gonna discuss saturation

and pooling patterns that we'd have at a crime scene.

Saturation and pooling patterns

could tell us that someone is bleeding

at a certain part in a crime scene

for a period of time.

Sometimes when we see bubbles at a scene,

that could mean that we have an expiated pattern

or a pattern that's coming from an airway

but let's pop those because we don't want.

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 we'll see this on mattresses

or beds or bedding and then it would absorb

a little more.

Now we're gonna have an accumulation of blood

on a non porus surface and we'll see pooling.

Pooling and saturation, it's the same mechanism

that we'll looking at,

just accumulation of blood.

But with pooling, the blood is not being absorbed

into the surface.

For pools of blood what we'll see with actual whole blood

that has fibrin in it, they will dry a lot slower

than it would in something that's absorbent,

but also we're gonna see over a period of time

is clotting inside that pool.

And then sometimes we'll see effect what's called

serum separation, so the edges of this would be clear

where we'd see the plasma of the blood

as it separates.

Now we're moving onto the spatter category

of bloodstain pattern analysis.

With this category of bloodstains,

we're looking at some sort of external force

on an open source of blood.

So what I'm gonna do is I'm gonna put

a small amount of blood on our wood here,

I'm gonna strike it with a hammer

and then what we should see is that impact spatter

on the plexiglass in front of us.

Put on my googles,

I'm gonna put my hood up.

Get us a small amount of blood here.

All right, ready?

There we go.

So as you can see [laughing]

not only do we have impact spatter

on the plexiglass in front of us.

We also have it on our suspect here.

We applied force to an open source of blood

and we have a resulting impact stain.

Our stain pattern, what we will notice is

directly opposite where the force was applied

we have our blood striking that surface at 90 degrees.

These stains that we have right here

near the bottom are circular

but the further we move away from that source,

these bloodstains are now hitting this surface

at an angle so our stains are more elliptical.

Bludgeoning would be the most common way

that we get these stains

but it could be that we have

the force of a bullet passing through somebody,

so we have a phenomenon called forward spatter

and back spatter.

So if someone is shot and the bullet

passes through say their shoulder,

we have blood going in the direction of the force,

so with the bullet out of the exit,

but we also have blood going the opposition of the force,

and that's what we call back spatter.

First off we started by creating different patterns

so that we could analyze.

Next step, we're gonna at something a little more difficult.

Next we do is calculate the area of convergence.

That's the two dimensional area on our surface.

If we draw a line through the long axis

of several stains where all these lines will meet.

They should converge in an area

somewhere in the center here.

What I wanna do is pick several stains

that are elliptical from different sides of the pattern.

We're looking at this to solve where this blood came from.

I'm gonna start with this stain here

and I'm going to line up so that I'm drawing

a line through the long axis of my stain.

So this is where the tail is gonna help me out

to figure out the directionality,

but also to line up my ruler.

And then sometimes what we'll do

is just kind of show for a jury an arrow,

the direction that stain was going.

Then I'll move around a pattern from different sides of it

and draw through different stains.

This isn't done on every crime scene but when we have

a pattern like this that we have elliptical stains

along the outside and we have some

circular stains towards the inside,

this is the perfect opportunity

for us to do some analysis.

I could keep going and draw more lines

for more stains and it should all be coming back

to the same general direction.

If this was on the wall

and this was very low,

this could be very powerful evidence

to show that that was low to the ground

where this impact happened.

Since we identified different stains

that are striking our surface at different angles,

we're gonna figure out the angle of impact

that these stains hit our surface.

We do that by measuring the length of the stain,

we divide it into the width of the stain

and the arc sin of that number

will give us our angle of impact.

So when we're measuring stains,

we always wanna use millimeters.

Allows us for smaller measurements

so what we could also use is a digital caliper

and that will give us precise,

sub millimeter measurements.

So I wanna measure the length of the stain,

long axis of the stain, so this is 3.1 millimeters.

And then I'd measure the width of it

so I'm measuring the widest part of the stain.

That's 1.7 millimeters.

We're gonna divide 3.1 into 1.7

so if we do the arc sin of that number,

that'll give us the angle of impact,

which is 33.25.

If you had a regular ruler,

you would just have to round up to

the closest millimeter, so in this case,

this stain is four millimeters,

and then we'd measure the width of it.

It is two millimeters.

So we would divide four into two

which gives us .5 and the arc sin of .5 is 30 degrees.

And we can see this basically at the same distance

from our center, but just on the other side.

If we look at this two dimensionally,

we know that these lines of our area of convergence

meet here but if we wanna think about it

three dimensionally that my blood is coming from

somewhere above it here.

The next step will be that we're gonna

calculate the area of origin.

If it's coming at a right angle here,

I have a triangle.

So this would be my adjacent side of the triangle.

I know that it's 90 degrees from here,

so that's my right triangle

and then this side that the path takes

is the hypotenuse of the triangle

and so if I know the distance from my stain

to my area of convergence

and I wanna figure out how far away

my area of origin is here in space,

if I do the tangent of that,

I could figure out the side, like sohcahtoa.

When we analyze bloodstains in the field,

I always feel it's better to do all these methods.

We should coming out with similar results

but if you messed up somewhere,

one of those is gonna be correct.

Next up we're gonna try something

a little more difficult, interpreting relationships.

There's an adage that forensic science

is the art of observation governed by science.

So we have observed our stain patterns at our crime scene

and we're gonna interpret how these possibly were created.

If I go to a crime scene and I see that

there's some clothing there,

eventually I'm gonna recover this,

but after I recover it and I see that

there's passive stains underneath it,

I know that this came after this.

That this wasn't in place,

that this was placed afterwards

and if I don't see a transfer of blood on here,

it could be that this was already dry

by the time this clothing went on top of it.

Now we're looking at a passive drip pattern.

This could be the victim's blood,

this could be the suspect's blood.

We won't know until we sample it

and send it off for analysis.

What we can interpret from this could be movement.

So if this trail of blood is leading away from the scene,

we would see those tails going in a direction of travel.

Now we're looking at a wipe pattern.

We have a pre-existing stain that something

came in contact and moved through it.

So we could see from our discussion earlier of feathering

that the directionality is coming towards me.

Something is passively dripping blood.

That could be a weapon, that could be a victim,

that could be our suspect

and then something later on comes through it.

That could be someone trying to clean up the stain.

This could also be that maybe someone

was dragged through this or there was

some sort of movement through that stain.

That was a wipe pattern, now we have a swipe pattern.

Blood is on something here and we can see that again

that same feathering going in the direction of travel.

We have a transfer pattern with movement

which is a swipe pattern.

There's blood on something

and then we're just moving that in a direction.

Usually when it's a wipe pattern,

we could see those original stains,

so they're drying and then someone tries to

wipe them off with a cloth.

Now we're looking at a cast off pattern,

so this is a sub-category of spatter

that's a projection mechanism,

so blood is on an object and we're moving

that object in space.

That could be someone's hand,

that could be a pipe,

that could be a bat, that could be a knife

and as that object moves,

blood will be flung off it

and we have these very distinct linear patterns

or curvy linear patterns.

At a crime scene if we see these cast off patterns,

they can go up the walls,

they can go across the floor

and even onto the ceiling.

We're looking at a spatter pattern,

but we have a normally continuous drops of blood

that are being interrupted

or blocked by something and that gives us

a pattern that's called the void.

Sometimes we have crime scenes where

there's something important

that would be in that pool or in that pattern

or that spatter pattern and it's been removed.

So it could be someone's bag

or a cell phone, their wallet.

I had a crime scene where someone was bludgeoned

and adjacent to his head was the complete absence

of blood spatter.

Looking to the left of him,

there was a spatter pattern that didn't line up.

What we determined was that the curtains

inside of the hotel room were open

at the time of the crime and then closed later on.

We've gone over how these patterns are created,

our different categories of patterns

and what we can interpret from these patterns

at a crime scene.

This is not a simple process.

This stuff takes time, training, and experience

and beyond that, there's no absolutes with any of this.

There's no one specific answer

then it's only that one answer.

I hope you guys learned a lot.

[applauding]