Hi, I'm Matt Steiner.

[Narrator] Matt is a certified senior crime scene analyst.

He's demonstrated how to lift fingerprints

and analyze bloodstain patterns

in Technique Tutorial. There we go.

Today, I'm gonna show you how

forensic analysts determine bullet trajectory.

[gentle music]

[Narrator] In this episode, we'll learn

the methods experts use to investigate a shooting scene,

increasing the complexity with each step.

Firearms are used at many crime scenes, so to

analyze the evidence that's left behind is very important.

Before we can start plotting a bullet's trajectory,

we need to know something about ballistics.

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Ballistics is the analysis of a projectile in motion.

Forensic ballistics focuses on firearms-related projectiles.

There's internal ballistics, external

ballistics, and terminal ballistics.

Internal ballistics is what happens inside that gun.

External ballistics is what happens to that bullet

once it leaves the muzzle of that weapon.

And finally, terminal ballistics is what happens

when that bullet strikes that target.

Understanding these three categories,

it's important because they're all related.

That bullet that comes from the gun

takes a path and then goes into a surface.

When we go and testify in front of

a jury, we have to educate them.

They don't know the difference between a cartridge,

a casing, and a bullet, and they're three different things.

So, what we have here are unfired cartridges.

These would go inside of a weapon

and then, when they are fired,

they are separated into different components.

So, now we're looking at shell casings.

After we fire that cartridge, this is either gonna

remain inside the weapon or be ejected outta the weapon.

When that cartridge casing is fired,

the bullet is gonna come outta the barrel of the weapon.

This bullet is in pretty pristine condition.

I believe this one was fired into a tank of water

and recovered, so we don't see a lot of deformation on it,

but I do see the rifling on that bullet,

so I know it was fired from a weapon.

As these bullets strike different targets,

they're gonna deform in different ways.

They flatten out, they hit an object at an angle

and are dented, or they pass through something soft,

like this bullet and that bullet,

and then sometimes when these bullets

hit surfaces, they will fragment.

When we're at a crime scene, tasked to determine if we have

ballistic trajectories or if we have ballistic damage there,

the presence of a bullet, and especially a bullet

that's been damaged, could help us in figuring out

whether that damage was created by

a bullet or from some other means.

Next up, we're gonna show how

these bullets show up at a crime scene.

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Now that we've seen cartridges, casings, and bullets,

let's see how they affect our crime scene.

So, when we encounter ballistic damage at a crime scene,

we wanna first figure out, if we have a hole,

what is the entrance and what is the exit.

So, if we look around the perimeter

of our entrance, we see a dark substance.

This is what's called bullet wipe.

As that bullet travels down a barrel,

we have burnt gunshot residue and residue inside the barrel

that's being picked up on that bullet

as it travels from the muzzle of the weapon

and as it passes through our surface,

it wipes that residue off.

So, if I had a bullet that enters on this side,

exits on that side, re-enters another surface and re-exits,

I could tell which side it entered first

because it doesn't have any more residue to wipe off.

With the exit, we can see here that the fibers of the wood

are going in the direction of the bullet.

Plywood's a little different than solid wood would be,

but with this or with metal, we would see

that substrate pushed in a direction of the exit,

where on the entrance side, we would see it pushed in.

So, when I look at this bullet hole entry,

I could tell its directionality.

Understanding directionality is one of the keys

to figuring out what happened and how it happened.

What I see is the parabolic shape of the bullet

as it first comes in contact with the surface

and I know it's traveling from

left to right because of that U shape.

Another clue to directionality for us, by looking at this,

is on this bullet hole where the bullet doesn't actually

penetrate the surface but glances along it.

Can first tell its directionality by first looking at

that U shape, that parabolic shape,

and then what we also notice is that

the shape is very symmetrical on the front of it,

but as it's traveling from

left to right, it becomes asymmetrical.

So, that bullet is being deformed as it's moving along

the surface, creating this asymmetrical damage.

We just talked about directionality

as it relates to entrances and exits.

Now we're gonna add a layer of complexity to it.

So, on a car door, we could see that bullets are

coming from a couple different directions.

So, we can tell these are all entrances because the way

the metal is deforming in the direction of the bullet.

We have very circular entrance holes here, here, and here.

These shots are coming pretty straight on,

perpendicular to that surface.

With our bullet hole entry that's going

from right to left here, I know it's going

that way because of certain key clues.

What I'm looking at is the point that

the bullet strikes the surface first and creates

a shoulder that goes into the car door.

So, another key to directionality on

this first bullet hole entry is that we have

an area of preserved paint right at the edge here.

So, that's called a pinch point.

So, the pinch point is where the bullet

first comes into contact with the painted door

and it's preserving that area and then,

as the bullet travels further,

in this case from right to left,

it's gonna enter the car door and create damage.

So, we see that the paint has flaked off around it,

but it's being preserved right here

where the pinch point is.

Next, we're gonna calculate the angles

in which this bullet entered this car door.

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At a crime scene, we measure out

the specific locations of each bullet hole entry

and ballistic impact mark, fixing it to the world.

So, from the ground to an edge of a door to a wall.

This is used quite frequently in

shooting reconstruction cases where we

wanna show where that bullet is coming from.

So, this can be time consuming.

On big scenes where we have a lotta evidence,

we may want someone who's just trained in this

to do this sorta work 'cause this could take hours.

First, we're gonna calculate the vertical angle.

We use an inclinometer or a

digital inclinometer to get this measurement.

So right now, we have a measurement of 10 degrees downward.

Next, we're gonna calculate the azimuth angle.

That's the left to right or the right to left angle.

So, what we wanna do is place our

zero point at 90 degrees, there's a line there.

Lining up exactly where that

bullet strikes the surface first.

I'm gonna have Johnathan come in

and give me a hand with this.

Next, we're gonna take a plumb bob

and on the interior side of that angle,

we're gonna drop it and hold it

alongside our zero-based protractor.

Our line is striking the zero-based protractor

at somewhere around 23 degrees.

We would document this as traveling

from right to left 23 degrees.

Now, we're gonna attach a laser to

the end of our trajectory rod to visualize its trajectory.

This is used quite frequently

in shooting reconstruction cases where we

wanna show where that bullet is coming from.

So, in order to see this and document it

through photography, we're gonna have to dim the lights.

[light switch clicking]

So, I'm spraying along the line.

If I was photographing it, I would do

a long exposure so this'd be captured over time.

[spray can hissing]

Another method to show this trajectory line

would be to reflect light back towards the camera

by reflecting it off a white card.

And over time, if I did a long exposure,

I could show that line.

[light switch clicking]

So, if I had this as evidence at a crime scene,

our bullet hole entries, we'd put

a trajectory rod in for each one.

The more ballistic damage we have,

the more work it's gonna be.

If I had a case, let's say, where a bullet

came through a window and struck a wall

but didn't enter the wall, I could

do trajectory with that with string.

I'd attach one end of the string to the damage on the wall

and then bring that string and run it

through the hole in the window and that also would

give us the area where that bullet came from.

The advantage of string is that

it's easy to photograph during daylight,

where the laser, we'd have to make the area dark

and then, that's not possible when the sun is out.

We just finished with lasers.

Our next step is to use the 3D laser scanner.

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So, we're gonna be using

the Leica RTC360 to capture our crime scene.

So, with the laser scanner and with the Leica software,

not only can we get very precise measurements,

we can also get those same angles

that we calculated with a trajectory rod.

So, we're gonna set up our laser scanner

in two different positions and scan this scene.

After we scan the scene, we're then gonna import that data

into software so we can visualize our point cloud.

So now that we have our two scans,

we've imported it into our Leica software.

Anything that's in the view

of the scanner is gonna be captured.

So, you can see us off set here.

There's me.

So, the RTC360 could take about

two million measurements per second.

So, as it spins a full 360, all these measurements

will look like one large point cloud.

The beauty of laser scanning is that,

unlike a static image, we can move it around,

we could view it from different angles,

we could see these trajectory rods that we have in place,

and we can get novel views of the scene

that we couldn't get with traditional video or photography.

And one of the great things about

laser scanning is that it's objective.

Any other type of measurements

that we take at a crime scene,

I'm choosing to measure from two points

or three points to this evidence.

With the Leica scan, anything that's

in its field of view, it's documenting it.

So, we may not know that something over here

is valuable and we don't collect it,

we don't photograph it, and we miss it.

But later on, as our investigation proceeds, we find out,

oh, this was really important.

At least it's captured with the laser scanner.

What also we could show with this is our cone of tolerance.

So, with trajectory analysis, there's a built in

plus or minus five degrees of error.

With this software, I could show that error.

So, I've created a line from two points on that rod

and now I could take that line and extend it out into space.

And sometimes in real crime scenes,

this becomes very important.

I had a reconstruction that we did where a bullet

went through the 13th floor window of a business

and they wanted to see where that bullet came from.

So, we scanned inside of the business

and in several blocks around it on the street

and were able to trace that trajectory

about 800 feet away, two blocks away from the locations.

So, today we talked about the basics of ballistic analysis.

These skills are built over time,

taking hundreds of hours of courses,

more scenes, more experience, and the better you get at it.

Hopefully our viewers have a better understanding

of shooting reconstruction as well as

the physics, math, and science behind it.

I find bullet trajectory fascinating and I hope you do.

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