1

Mrs. Svedstrup

Firearms and Toolmarks Chapter 9

2

• Tool Marks – scratch or other microscopic marking left by action of tool on an object

• Examples include impressions left by blade or wire cutter on end of cut wire or scraping of screw driver on door jamb

• Firearms Identification involves analysis of marks on bullets or cartridge cases due to the mechanisms within the weapon

Firearms and Toolmarks

3

• 2002 ATF reported 80,000 weapons sold illegally in U.S.

• 2000 people were charged with selling guns illegally

• 350,000 firearms related crimes are committed each year

Firearms Identification

4

• Identify bullets and cartridge cases—test fired evidence to crime scene evidence

• Use tests to determine whether a weapon has been fired

• Can estimate distance of shooting incidents

• Chemically restore obliterated serial numbers

• Test items/people for gun shot residue (GSR)

• Analyze patterns of injury—wound ballistics

Firearms Examiners

5

Pistols- self-loading or revolvers

Rifles Machine guns

Submachine guns

Shotguns

Types of Firearms

6

• Creates “spin” of bullet as it emerges from barrel

• Spin creates angular momentum to the bullet allowing it to achieve the desired trajectory

• Consists of a series of land and grooves

Rifling of a Gun Barrel

Land

Groove

7

• Rifling button or gang broach are used to dig grooves into inner surface of barrel

• Grooves are dug in a spiral fashion

• Lands in the barrel create grooves on the bullet as it travels and likewise grooves in the barrel create lands on the bullet as it moves through the barrel

• Any wear patterns or imperfections in the broach make each barrel unique.

• These imperfections are transferred to the bullet, giving it individual, unique characteristics.

Rifling of a Gun Barrel

Slant give spiral to the barrel groove

8

• Size of rifled firearms: caliber or bore diameter

• Bore diameter: distance from opposing lands

• Caliber describes size of a particular cartridge

• Shotguns are measured by their gauge

• Gauge refers to number or pellets weighing one pound that would have same diameter as barrel if grouped in a circular pattern

Size of Ammunition and Barrels

9

• A live round is a bullet fitted into a cartridge case with unfired gunpowder

• Gunpowder takes up the lower half of the cartridge

• Primer is the pressure sensitive explosive mixture fitted in a cup below the gunpowder

• Cannelures are small grooves that circle bullet and hold it in place

The Anatomy of a Live Round

Bullet

Casing

Powder

Primer

10

• Three types of bullets: • Lead or lead alloy

• Fully-jacketed bullets

• Half-jacketed bullets (jacketed soft points & hollow points)

Types of Bullets

11

• Black powder is oldest recorded propellant and was invented by Chinese around 10th century

• Consists of a mixture of charcoal, sulfur, and saltpeter

• Smokeless powder comes in two types:

• Single base

• Double base

Propellants

12

• James Forsythe, Scottish Clergyman, discovered mercury fulminate, which was used by 1850 in cartridges

• Primer is shock-sensitive chemical compound that explodes, igniting the secondary gunpowder charge

• Primers have continued to change and evolve

• Potassium chlorate was next prominent primer

• Lead styphnate, antimony sulfide, barium nitrate and tetracene are now used

Primers

Primer cup location on base of cartridge

13

• Head of cartridges may have manufacturer markings

• Extractors, ejectors, firing pins and breech blocks may all leave impressions on cartridge case

Cartridge Case Characteristics

14

• Firearms evidence must be clearly documented and photographed

• Portions of walls or items containing cartridges should be removed

• Care must be taken not to mark or deface bullets or cartridges when collecting them-do not use metal tools!

• Bullets & cartridge casings should never be marked, but put in small vial or box and tagged

Crime Scene Processing

15

• Weapons can be a significant

source of trace evidence

• Blood, fibers, fingerprints,

bits of tissue,

or paint flecks may be present

• Weapons should be identified, especially determination of serial number

Preliminary Examination

Packaging a weapon

16

• Need to collect samples for comparison

• May need to fire weapon into bullet trap

• Ammunition used must be of questioned type

• Class characteristics of bullets include caliber, number of lands and grooves, and their angle and direction of twist

• If class characteristics match, then examiner compares individual characteristics—matching striations in the grooves of the bullet

Bullet and Cartridge Comparison

17

Class and individual characteristics of a fired bullet.

Twist

Caliber

Land

Groove

striations

18

• Use of a comparison microscope is necessary

• Interchangeable barrels, rust, and stria from bullet can impede matching

Bullet and Cartridge Comparison

19

• Markings on cartridge cases include

• firing pin impressions

• extractor and ejector markings

(except in revolvers)

• breech face markings

• chamber markings

Cartridge Cases

Firing pin impression and breech face marks

Parallel markings from breech face

Extractor Marks

Ejector Marks

Chamber Marks

20

• 1993 FBI began DRUGFIRE system

• Database of firing pin and primer impressions on spent cartridges recovered from crime scenes

• Computer network allows firearms examiners to search database for impressions

Digital Imaging Systems for Ammunition

21

• Developed by BATF (Bureau of Alcohol, Tobacco, and Firearms) to capture and rapidly compare bullet stria

• In 1997 FBI and ATF established the National Integrated Ballistic Information Network (NIBIN)

• NIBIN allows searching of bullets or cartridges using the same computer system

• Led to concept of ballistic fingerprinting

Integrated Ballistics Identification System (IBIS)

22

• Hot gases and powder are discharged from firearm when a bullet is discharged

• Known as gunshot residue (GSR)

• Depending upon distance, approximate distance between weapon and target may be approximated by size of GSR pattern

Distance of Fire Determinations

A = Contusion Ring

B = Ring of Dirt

C = Stippling

D = Soot from Gunpowder

23

• Limitations of GSR test

• GSR rarely travels more than 18 inches

• No GSR is found on distance shots

• GSR is found on target in close range shots

• GSR is usually is embedded in flesh in contact shots

• Distance shots produce contusion rings that do not change with distance

Gunshot Residue Test

www.firearmsid.com

24

• As shot leaves barrel, it creates a conical pattern

• Size of pattern increases as distance increases

• It is difficult to establish accurate pellet patterns due to the targets they hit or miss—(humans can be smaller than the pellet spray

• Contact with intermediate targets can skew pattern

Shotgun Shots

www.firearmsid.com

close distant

25

• Defined as a scratch or other microscopic marking left by the action of a tool or an object

• Tool marks can be individualizable - tools wear with use and get scratched and nicked

• Criterion of match of known and unknown toolmarks is that there must be a significant number of similarities and no unexplainable differences

• Virtually any tool can leave their markings

Toolmarks

26

Comparison of two cut wires.

The wire on the left (red circle) is not a match to the tool

The wire on the right (blue circle) is a match to the tool

Comparison of toolmarks made by the same metal tool. Note how the striations line up left to right.

27

Serial Number Restoration: Stamping a Serial Number in Metal

a

b

c

a: Number stamped into metal

b: Metal around number is ground down

Number disappears

c: Metal under number dissolves faster when

numbers restoration solution is applied

28

• Serial numbers are stamped into an object that is usually metal

• Serial numbers are applied to an iron or steel surface

• Hydrochloric acid, water and cupric chloride solution is a common means to recover serial numbers

Serial Number Restoration

29

Serial Number Restoration

A. Before Restoration

B. Chemical Treatment

C. After Restoration

30

• Once the serial number is visible it must be photographed, as it will fade from view with time

Serial Number Restoration