Chapter 9 (Firearms, Tool and Other Impressions) (copy)

How do you identify firearms?

Involves:

Comparison of bullets

Restoration of obliterated serial numbers

Detection and characterization of gun powder residues on garments

Estimation of muzzle-to-target distances.

Trigger pull

Functionality

what are the types of firearms?

Single-shot handguns

Revolvers

Semiautomatic pistols

Firearm and Ballistic Evidence

Contains both class and individual characteristics

Examine:

Gunshot residues = Find distance determinations.

Weapons

Casings

Bullets

Unexpended cartridges = Link them to an object, or associate them to each other.

Projectile

Bullet

Cartridges are?

Center fire or rim fire.

Handguns

Revolver ( ammunition is hand inserted ) or pistol which is magazine fed.

Rifles

One cartridge or magazine fed.

Shotguns

One, two or magazine fed

All of the guns (Rifles and Handguns) have rifled barrels except?

Shot guns ( smooth bore).

What makeup the rifling of the barrel?

Lands (Raised: Projections) and Grooves (Lower: Depressions)

Cut into the softer lead bullet and produce microscopic striations

NO two rifled barrels, even those manufactured in succession, have identical
striation markings.

These striations form the individual characteristics of the barrel (T/F)

True

Pistol Cartridges contain?

Bullet

Casing

Powder

Shotgun Cartridges contain?

Metal and Plastic Casing

Paper and Plastic Wadding or Shot Shell Cups

Shot Pellets

Powder

What causes the projectile to twist, thus causing stability in the air as the projectile travels.

Rifling (Adds individualizing striations to projectile)

Class characteristics of Firearms

Caliber (diameter of the bore) from casing

Shape of the firing chamber

Location of the firing pin

Shape of the extraction or ejecting mechanism

Direction of twist by looking at barrel

Number, size and direction of twist associated with lands and grooves.

Recovered casing will also contain what marks across the base of the casing?

Breech bolt

In addition to Breech bolt marks, what other marks may be seen?

Ejector and extractor marks

Comparison of theses marks may allow exclusion or individualization.

What may be compared to each other to determine if one or multiple weapons were used?

Casings

How do you handle collecting casings?

Gather them up separately and do not mark them.

Place each item separately and notate where the item was located.

At scene before sending them to the lab, all firearms should be made safe. (T/F)

True

Who will determine individualizing characteristics of firearms?

A forensic firearm and tool mark examiner

What are individualizing characteristics for firearms?

Breech-face marks

Land impression

Breechface markings are caused by?

Force generated as the bullet is fired in the forward direction (Equal but opposite fore presses back causing the back of the casing to press against the breechface)

Firing pin marks are also left on the?

Primer

What other marks are also made by the mechanical system to retain & push out the spent cartridge?

Extractor and ejector marks

Extractor is the _____
Ejector is the __________

Extractor is the hook
Ejector is the metal protrusion

Automated search system by the FBI

DRUGFIRE

Automated search system by the ATF

Integrated Ballistic identification system (IBIS)

In 1999: Both IBIS and DRUGFIRE combined to create the?

National Integrated ballistics information Network (NIBIN)

The distribution of gunpowder particles and other discharge residues around the bullet hole permits an assessment of the distance from which a handgun or rifle was fired

Distance determination

A more exact determination is made when?

Weapon and ammunition used are recovered.

Then proper analyses can be made.

For distance determination, what will the firearms examiner do?

Several test shots to compare the spread of the gases and unburned particle to the victim’s pattern.

Contact or less than 1 inch

Heavy concentration of vaporous lead surrounds the bullet hole

Loose fibers show scorch marks from flame discharge of the weapon

Synthetic fibers may show signs of melting from heat effects of discharge

Stellate tear pattern may appear on clothing.

The hole is also surrounded by a rim of a smoke-like deposit of vaporous lead.

12-18 inches

Halo of vaporous lead deposited around the bullet hole.

Around 25-36 inches

No soot but a presence of scattered specks of unburned or partially burned powder grains.

3 ft or more

Bullet hole with a bullet wipe mark (a dark ring around the entrance hole)

Primers contain:

Lead

Antimony

Barium

Two main tests to tests for primer residue are?

Atomic absorption

SEM

What do you do for the Atomic Absorption Test?

Swabbing the hands with 5% nitric acid. Both hands (front and back)

Then sent to the lab for analysis (AA) to detect high barium and antimony levels

Describe the SEM Test:

SEM testing from adhesive stub

Show fused particles of the elements

Stamped on many surfaces that may be involved in a crime like guns, and parts of a car.

Serial number

Many thieves try and obliterate serial numbers to keep the investigators from tracing the weapon or car back to the original owner or previous owner. (T/F)

True

The firearm/toolmark scientist has the tools to recover obliterated serial numbers by?

Etching the metal away and revealing the metal below the imprinted surface that has the imprint available.

In other words: Below a stamped number -a different crystal formation of the metal that is easier to etch out with acids, revealing the imprint even though one can not directly see it.

How do you collect and preserve Firearms?

Safety is most important: You don’t want a unexpected discharge of a weapon.

Weapons must be unloaded

Documentation must show the exact location of the ammunition (fired and unfired).

Place each round in a separate container.

How do you collect and preserve Ammunition?

Primary Conern: Protect class and individual characteristics

If bullet is lodged in a wall: Break away material surrounding the projectile until is loosely comes out (Or take piece of wall with you to lab)

Bullets must be preserved for trace evidence within it.

Wrap bullet with tissue (kimwipe).

Ejected casing from a semi-automatic pistol must be documented showing the?

Relational detail of casing spread to firearm to victim.

How do you collect and preserve Gunpowder deposit?

Preserved and protected from rubbing any other item

Place each item separately into a paper bag.

Any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object.

Toolmark

Most impressions leave class characteristics but when they do leave discernible nicks and breaks, it is because the tool has acquired?

Wear and use (the history of the object).

Provide individualizing characteristics to the tool mark.

How do you collect the tools and toolmarks?

Submission of the entire object that has the tool mark (when impractical the toolmark can be casted)

Photography will be used as documentation, with a scale.

Packaging the tool (if found) and the tool mark. (Do not attempt to place the tool into the tool mark.)

What are other impressions that can also be left at the crime scene?

Shoe

Tire

Fabric

Preserving the impression involves what?

1. Photography first

2. Lifting or casting the impression.

Lifting may involve an ________________________ to lift footprints.

Electrostatic dust lifter or sticky material

Casting involves the addition of ____________ to make a cast of your foot or shoe print

Dental stone (slurry)

Sometimes bloody footprints need chemical agents to develop it (T/F)

True

What are the class characteristics of Tires?

Tread

Width

What are the individual characteristics of Tires?

Wear and damage