Arson and Ballistics

v

pattern of typical fire

accelerant

any material used to start or sustain a fire

Number of kids Cameron Willingham was convicted of killing

3

arson

intensional setting of fire

lightning strike

a natural fire

Hydrocarbon detector

Used to detect accelerants

exothermic

releases energy

Gas Chromatography

analyze accelerant residue

reason for most arson

isurance money

product of fire

heat and light

hydrocarbon

A compound that contains only carbon and hydrogen atoms

murder

the intentional killing of another person

point of origin

The location where the fire started

Oxidation

addition of oxygen

Package for arson evidence

Sealable can

Role of arson investigator

identify, detect

prolysis

decomp of organic matter by heat

arsonist

person that sets fires

factors that influence behavior of fires

Fuel
Weather
Humidity
Oxygen concentration
Shape of terrain

affect fuel as it relates to fire

Type of fire
Size of fire
Surface area of a fire
Heat produced as a fire
Amount of fuel
The moisture content

backdraft

a situation where there is a low concentration of oxygen is called backdraught
enclosed fire has used up most of the oxygen and is just smouldering. If there is a sudden influx of oxygen (like someone opening a door or window), the fire will immediately explode into flame

humidity's affect on fire

If relative humidity is low, it will contribute to the drying of fuels. If it is high, fuels will absorb moisture from the air, making ignition more difficult.

Three requirements must be satisfied to initiate and sustain combustion:

fuel, oxygen, heat

When a RAPID combination of oxygen and other substances combine, _______ occurs.

combustion

Once combustion begins, enough heat is liberated to keep the reaction going by itself. A fire becomes a _______ , absorbing a portion of its own heat to generate more heat.

chain reaction

several ways detectives find accelerants

Portable hydrocarbon detectors and/or swab
Accelerant sniffing dogs
Identifiable pour patterns (that are then tested)

When specimens are collected from a crime scene, they should be

packaged immediately in airtight containers so possible residues are not lost through evaporation

Common reasons for arson crimes:

Insurance fraud -- $$$
Crime concealment
Pyromania
Revenge

Many U.S. state legal systems and the legal systems of several other countries divide arson into degrees..... which are

First-degree arson - Burning an occupied structure such as a school or a place where people are normally present
Second-degree arson - Burning an unoccupied building such as an empty barn or an unoccupied house or other structure in order to claim insurance on such property
Third-degree arson - Burning an abandoned building or an abandoned area, such as a field, forest or woods.

Ballistics

simply stated is the study of bullets and firearms.

Firearm

a weapon capable of firing a projectile using a confined explosive.

Ballistics can tell investigators:

type of firearm used
caliber of bullet (internal diameter or bore of a gun barrel)
# of bullets fired
where shooter was standing
angle of impact from shooter to victim
if firearm was used in previous crime

Hand Gun

pistols & revolvers
can fire with one hand
can be further classified as semi-automatic (fire one bullet per pull of trigger) or fully automatic (fire repeatedly as long as trigger is pressed)

Long Gun

rifles and shotguns
require 2 hands, shoulder use
rifles fire bullets
shotguns fire pellets (multiple projectiles) or a slug (single projectile

Parts of a cartridge

1- Bullet
2-Casing
3-GunPowder
4-Rim (external flange/grip casing when removed from the chamber)
5-Primer (ignites the propellent)

Anatomy of gun

trigger, Hammer, Grip, Barrel and Sight

How a Firearm Works

1. The trigger is pulled and firing pin from firearm hits the base of the cartridge, igniting the powder inside the bullet.
2. The pressure of the ignition pushes the bullet from the casing and into the barrel of the firearm.
3. The bullet follows the lands and grooves pattern of the barrel and spirals out of the barrel.

firearm identification

is a method used to determine if a particular bullet or cartridge was shot from a particular weapon.

Striations

scratch marks left on the projectile by the rifling lines of the inside of the barrel.
Each gun contains unique lands and grooves within the barrel, thus producing bullets with unique patterns.

Breech markings

marks left on spent cartridge casings.

Firing Pin Markings

The firing pin of a firearm will leave a unique stamping on the cartridge's primer/rim.

Gun Shot Residue

The amount of GSR decreases as the distance between firearm and victim increases & vice versa.
GSR can be removed by washing, but chemical tests can often detect residue despite attempted removal.

Bullet Trajectory

Investigators may also be able to calculate a bullet's path or trajectory to find the location of a shooter.
This requires investigators to understand how a bullet behaves once it leaves a weapon.