FIREARMS AND IMPRESSION EVIDENCE EXAM 10 TEST REVIEW

Define forensic Ballistics

Forensic ballistics is the examination of evidence relating to firearms at a crime scene

What invention led to the invention of firearms? Where did this discovery take place?

The invention of gunpowder in china perceded the invention of firearms. Advances in physics, chemistry and engineering were also needed to produce modern firearms.

Define Handgun

Handguns: Short barrels, designed to be held in one hand, thick walls to withstand high pressures.

(Often rifled, limited in accuracy. Typically used for firing at stationary targets.

Define Rifle

Long barrels with rifling and thick walls to withstand high pressures.

(Rfling puts a spiral spin on a bullet fired from a rifle, increasing accuracy and distance. Typically used for firing at stationary targets)

Define Shotgun

Long barrel, smooth bore and thinner walls. Typically used for firing at moving targets.

What is Rifling and its importance to forensic science?

Rifling refers to the spiral grooves on the inside of a rifle barrel (bore). Rifling produces characteristic markings- land and grooves on the bullet which can be used to determine the type of weapon used in a crime.

Define Caliber

Caliber refers to the diameter of a bullet (mm or cm).

What are the individual characteristics of bullets?

Weight, dimensions, (including caliber), shape, type, and rifling.

What are the class characteristics of bullets?

Striae, unique machining marks, and wear patterns.

What are the individual characteristics of cartridges?

Dimensions of shell casing, headstamp, wether it is center or rim fire.

What are the class characteristics of cartridges?

Unique markings created by the firing pin, ejector, extractor, breech, and chamber

What unique equipment is needed to compare unknown samples from the crime scene to known samples?

A comparison microscope.

What does gunshot residue (GSR) consist of?

GSR consists of ejector particles, combustion residues of the powder (mostly nitrates), and any unburned powder particles.

Where is GSR found?

GSR is carried forward beyond the muzzle and blowback dis[erses GSR backward toward the shooter.

What test is used to determine the presence of GSR?

The Griess Test is a color test for the presence of nitrates (NO3-) in the combustion products

What type of information is stored in the National Integrated Ballistic Information Network (NIBIN) and what is the network used for?

The NIBIN is a forensic database that contains information regarding all bullets and casings that have been retrieved from crime scenes and test fires. The NIBIN matches link weapons to other crimes, events, or people to help solve crimes.

Define Plastic Impression

3D Impression

Define Latent Impression

Not visible without chemical enchancement

Define Visible Impression

Print left after comin in contact with a colored material

Define oblique lighting in photographing impression

Oblique lighting uses a light source positioned at a low angle. Oblique lighting is usually used to show detail by creating shadows on the surface of the evidence that cannot be seen from directly above.

What is the process of casting an impression?

1. Set up a dam if the impression is on a slope

2. Mix dry dental stone with water to create a pancake-batter consistency

3. Pour the mixture on the side of the impression (so you do not disturb it), allowing it to flow onto the impression

4. Wait 15 minutes before marking your initials or the case number into the drying cast

5. Wait at least 30 minutes before lifting the impression. Lift the impression by carefully digging around the cast

What are the individual characteristics of shoeprint evidence?

Tread pattern, brand model, size.

What are the class characteristics of shoeprint evidence?

Unique wear pattern, damages, pebble embedded in sole, custom shoes, etc.

What are the individual characteristics of toolmark evidence?

Size, shape, pattern of impression. (basic features that define the tool)

What are the class characteristics of toolmark evidence?

Markings that arise over time form wear and tear, or markings made by the owner.