1. Ballistics

2. 1. Ballistics Shows Ballistic evidence helps explain:
What type of firearm was used
The caliber of the bullet used
The number of bullets fired
Where the shooter was located
Whether a weapon was fired recently
If a firearm was used in previous crimes

3. 2. Firearm History Gun Powder and Firearms
Chinese invented gunpowder over a thousand years ago for fireworks
It was later discovered that the explosive force could be directed down a cylinder
Muzzle loading matchlocks that used the wick to ignite the powder are invented
Percussion firing replaced the muzzle loading leading to cartridge and breach loading.
Modern weapons

4. 3. Modern firearms Modern Firearms are divided into 2 categories:
1. Long Guns
Require two hands for accurate firing
Rifles fire bullets
Shotguns fire pellets (shot) or single projectile (slug)
2. Handguns
Pistols are fired with one hand
Revolvers have a cylinder that usually holds six cartridges and can be fired in rapid succession

5. 3. Modern Firearms Automatic vs. Semi-Automatic weapons:
Semiautomatic weapons fire only one bullet per pull of the trigger
Automatic fire repeatedly as long as trigger is pressed

6. Pictures of Firearms Shotgun Rifle Revolver Fully Automatic
Semiautomatic
Forensic Science: Fundamentals & Investigations, Chapter 17

7. 4. Ballistics History
Goddard, Sacco and Vanzetti, and the valentine’s day massacre 1925
Comparison microscope invented by Goddard*
Northwestern University in Chicago sets up first crime lab
Now forensics can…
1. Compare bullets and match them to a specific firearm
2. Accurately estimate the distance of a shooting
3. Detect gunpowder residue around wounds and on shooters
4. Restore obliterated serial numbers

8. 4. Ballistics History Databases
Police upload information on bullet marks
Maryland forces each gun sale to first log a test fire into the system
Low success: only used in one case
2.6 million dollar cost
Crime Stats
Generally …
Harsher gun laws = higher crime rate
Lenient gun laws = lower crime rates WHY?

9. 5. Rifling
“Rifling” originally referred to the grooves or indentations on the rifle’s barrel
Grooves and ridges (lands) in the barrel of a gun produce the twisting that adds accuracy
Created during the
machining process
and changes with
regular use

10. 5. Rifling
Leaves a pattern on the bullet that is fired that is unique to that particular firearm
Rifling does change overtime as the gun is used and cleaned
Criminals can take “forensic counter measures” to try and conceal that their gun was the gun used in the commission of a crime.
Technology has allowed for ballistics experts to identify patterns of lands and grooves in pistols and rifles

11. 6. Bullets and Cartridges
Bullet- A projectile propelled from a firearm normally made of metal
Cartridge- A case that holds the bullet, primer powder, and gunpowder
The bullet is out front with the cartridge, holding the primer and propellant powders behind.

12. 7. Caliber
Measure of the diameter of the cartridge usually in hundredths or an inch
Common calibers include
.22, .25, .357, .38, .44, and .45
Example: .22-caliber cartridge measures 22/100 of an inch

13. 7. Caliber
European method of naming a firearm caliber uses the metric system
Ex. 9 mm firearms fire 9 mm bullets
Caliber also refers to the diameter of the inside of a firearm’s barrel

14. 7. Caliber
Why should the caliber of ammunition match the firearm that shoots it?
If they do not match, what could go wrong?

15. 8. Firearm mechanisms Sequence of events for firing a bullet
1. The firing pin hits the base of the cartridge, igniting the primer powder mixture
2. The primer powder sparks through the flash hole to the main propellant supply

16. 8. Firearm mechanisms Sequence of events for firing a bullet
3. The pressure of the explosion pushes the bullet from the casing into the barrel
4. The bullet follows the land and grooves spiraling out of the barrel

17. 9. Study of Bullets and casings
Process: you must answer three questions
1. How is each fired bullet marked?
2. What is the procedure to match a spent bullet to the firearm that shot it?
3. What makes up a test-firing, and why is it done?
1. Ballistics experts carefully examine used bullets and their spent cartridge casings for obvious markings left from the firearm that shot them
2. Investigators first get bullets and casings from the suspected firearm to compare to the crime scene bullets and casings
3. To get a known bullet for comparison, investigators test-fire the weapon into a water tank or gel block to be able to capture the bullet without damaging it.

18. 10. Marks on fired bullets
Rifling patterns on crime scene bullets are compared to suspected firearms
To acquire known bullets, suspects firearms are test-fired into water tank or gel block to avoid damage
Each gun has it’s own unique markings or rifling that is left on the bullet when it is fired.
Rifling can tell you
Without a comparison bullet: class evidence / manufacturer
With a comparison bullet: individual evidence / which gun fired
1. Ballistics experts carefully examine used bullets and their spent cartridge casings for obvious markings left from the firearm that shot them
2. Investigators first get bullets and casings from the suspected firearm to compare to the crime scene bullets and casings
3. To get a known bullet for comparison, investigators test-fire the weapon into a water tank or gel block to be able to capture the bullet without damaging it.

19. 11. Marks on the spent cartridge
Can also be used to identify the firearm used
Firing pin marks
Impression made on the bottom of the cartridge by the firing pin as it strikes the bottom of the cartridge
Breechblock marks
Marks produced when the cartridge slams backward and strikes the breechblock
1. Ballistics experts carefully examine used bullets and their spent cartridge casings for obvious markings left from the firearm that shot them
2. Investigators first get bullets and casings from the suspected firearm to compare to the crime scene bullets and casings
3. To get a known bullet for comparison, investigators test-fire the weapon into a water tank or gel block to be able to capture the bullet without damaging it.

20. 11. Marks on the spent cartridge
Can also be used to identify the firearm used
Extractor Marks
Minute scratches produced as the cartridges is placed in the firing chamber by the extractor
Ejector Marks
Minutes scratches produced as the cartridge is removed from the chamber by the ejector
1. Ballistics experts carefully examine used bullets and their spent cartridge casings for obvious markings left from the firearm that shot them
2. Investigators first get bullets and casings from the suspected firearm to compare to the crime scene bullets and casings
3. To get a known bullet for comparison, investigators test-fire the weapon into a water tank or gel block to be able to capture the bullet without damaging it.

21. 12. Gunshot residue (GSR)
Particles of unburned powder and traces of smoke
Contains nitrates and leaves traces on the hand, arm, face, hair or clothing of the shooter and or victim.
1. Ballistics experts carefully examine used bullets and their spent cartridge casings for obvious markings left from the firearm that shot them
2. Investigators first get bullets and casings from the suspected firearm to compare to the crime scene bullets and casings
3. To get a known bullet for comparison, investigators test-fire the weapon into a water tank or gel block to be able to capture the bullet without damaging it.

22. 12. Gunshot residue (GSR)
Investigators look for the presence of GSR when attempting to recreate a crime scene
Chemical testing can detect residue even if removal is attempted
Distance from victim to shooter can be determined by examining the residue pattern on the victim
GSR decreases as the distance between firearm and victim increases.
1. Ballistics experts carefully examine used bullets and their spent cartridge casings for obvious markings left from the firearm that shot them
2. Investigators first get bullets and casings from the suspected firearm to compare to the crime scene bullets and casings
3. To get a known bullet for comparison, investigators test-fire the weapon into a water tank or gel block to be able to capture the bullet without damaging it.

23. 13. Bullet Wounds Entrance wounds are smaller than exit wounds
Skin is elastic so it stretches as the bullet goes in and on the way out the bullet may be carrying body tissue and bone.
If the bullet penetrates clothing, what can fibers in the wound tell you?
Direction of penetration
Gunshot residue is found only on entrance wounds.

24. 13. Bullet Wounds
Stippling marks or “tattooing” can be found around the wound if the gun is fired touching or in close proximity to the skin when it is fired
Hot gases burn the skin
Entrance and exits holes do not always line up
As the bullet passes through the body it redirects depending on what it makes contact with
Bullets that do not exit the body generally cause more damage
Smaller bullets tend to stay in the body because they have less velocity.
1. Ballistics experts carefully examine used bullets and their spent cartridge casings for obvious markings left from the firearm that shot them
2. Investigators first get bullets and casings from the suspected firearm to compare to the crime scene bullets and casings
3. To get a known bullet for comparison, investigators test-fire the weapon into a water tank or gel block to be able to capture the bullet without damaging it.
Muzzle imprint

25. 14. Trajectory The path of the propelled bullet
Two reference points are needed to define the trajectory
Investigators can figure the shooter discharged the firearm somewhere along that line

26. 14. Trajectory Reference points can be
bullet holes in objects or victims
An entry point and exit point on a victim
Gunshot residue or spent cartridge casings
Lasers can trace a straight-line path to determine the position of the shooter
Why might trajectory be difficult to determine?
Trajectory may be difficult to determine because bullets ricochet, become damaged, and do not provide a direct path for measurement. Investigators may also have to use trace evidence such as footprints, fingerprints, or DNA evidence from hair or saliva to determine the shooter’s whereabouts ***Possible short answer question***

27. 15. Trajectory and Gravity
Two major forces acting on the bullet once it is fired
Forward force of the gunshot
Downward force of gravity
Wind speed, direction, and distance from target are factors that affect the adjustments the shooter will make to hit the target

28. 16. Determining Location of the shooter Trajectory
Use the Law of Tangents – TOA
Tangent (ᶿ) = opposite / adjacent
IF the angle is pointing upwards
Shooter was firing downwards and is positioned above the bullet hole
Add the height of the bullet to final answer
If the angel is pointing down
Shooter was firing upwards and is positioned below the bullet hole
Subtract the answer of your equation from the height of the bullet hole

29. 17. Trajectory Examples
Calculate the height of the shooter.

30. 17. Trajectory Examples
A shooter in a building fired upwards to into a neighboring office building. If the building he was in was 100ft from the neighboring building, the angle of the bullet hole was 50 degrees, and the height of the bullet was 100ft from the ground. How high was the shooter?