- 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.
[gentle music]
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.
[gentle music]
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.
[gentle music]
At a crime scene, we measure out
the specific location 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.
[gentle music]
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 location.
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.
[gentle music]