Week 10 - Firearms

Types of guns

Long arms - rifles, shot guns

Hand guns - revolvers, pistols

Machine/submachine guns

Air guns - low end of power but can still cause damage

Types of loading and firing

Manual - bolt action, pump action, single action revolvers, relatively slow, have to pull it back and put back into place before it can fire

Self-loading/semi-automatic

Cartridges

Made up of primer, propellant and the bullet. Primer causes the ignition, causing the gunpowder to explode within the confided space and shoot the bullet out

Shotgun cartridges

Made up of primer, propellant, pellets (like ball bearings which spread once fired so can hit a large area, increase likelihood of hitting something), card/plastic/fibre wadding

Components of ammunition

Primer, case, powder, bullet

Questions firearms examiners might need to answer

• What sort of gun was used

• Could a particular bullet/cartridge be linked to a certain crime

• Was it murder, accident, suicide

• Where was gun fired from

• Who fired the gun

• Where else has the gun been used

• Where has the gun come from

Stephen Paddock example

• Barricaded himself in hotel room with high powered rifles and shot from window down into a festival crowd

• 58 killed

• He also died

What is ballistics?

The study of projectiles, often separated into internal, terminal, and external

What is intermediate ballistics?

What happens as the bullets leave the barrel

Internal ballistics

What happens to the cartridge and bullet within the gun, marking from imperfections, unique indentations on the bullet caused by the barrel patterns (individualisation), marking on casings

Terminal ballistics

What happens as the projectile(s) hit/enter/exit the target. Jelly blocks are used to understand the impact of a bullet as they are similar to human flesh, gives insight into what is expected to happen as a bullet enters a human body

Internal damage caused by gunshots

Internal damage usually caused not by the bullet but by the amount of impact, the force involved, which causes a shockwave and damage to internal organs, can even break bones. If bullet hits something like a bone, it will start to spin and cause a bigger whirlpool, causing even more internal damage and a huge exit wound

Entry wounds

Usually neat as the fine point of the bullet entering something soft (fleshy part of the body)

Exit wounds

More messy, sometimes bringing internal matter and bone outside of the body

External ballistics

What happens between leaving the barrel and coming to rest. Where does the bullet go after exiting a body? Where does it go if the shooter misses? Issues of richochet?

Handgun types

Revolver and semiautomatic

Revolver

Has a barrel with 6 bullets, barrel rotates and as each bullet fires the barrel rolls around to align the next bullet, barrel has to be manually reloaded with bullets after all 6 have been fired. Can get shots fired quick timespan

Semiautomatic

As bullet exits gun, the energy from this is used to hook up the next bullet, force the ammunition up and expel the cartridge, 6-12 bullets, fires at a faster pace to the revolver, opportunity to use more shots

What might firearms evidence be examined for?

• DNA - from bullets

• Blood - from bullets

• Fibres - from clothing that a bullet may have gone through

• Indentations - serial numbers, even when attempts at removal (e.g. through Magnflux method/acid etching method)

National Ballistics Intelligence Services (NABIS)

Database that records details of ballistic items recovered, like a gun DNA database

Serial numbers

Legally held guns will have serial numbers. This is an important starting point to see who legally holds the gun. Chemical baths can be used to take off scrapes and reveal traces of the original serial numbers

Locating a firing point

• Placement of ejected cartridges, wadding etc.

• Use of string, thin rods, lasers etc. to indicate likely flight paths

• Modelling

• Entry and exit wound characteristics

• Use of GSR to indicate distance from target

• Scorch marks on skin = shot very close to target

Residue

When a gun is used it will produce types of discharge that lodge in things/people, telling us that something or someone has been exposed to gunfire

Gunshot residue (GSR)

Gas and particles formed from the primer, propellant and other tiny particles from the cartridge and gun. Deposited on individuals and things close by. Analysed for its presence and make-up using electron microscope

Other types of GSR

Firearms discharge residue (FDR), cartridge discharge residue (CDR)

What GSR can tell us

• Different ammunition produces different GSR, so helps identify the weapon

• GSR is difficult to wash off the skin and clothing, but has a short lived presence of several hours on human skin but longer on clothing and especially in pockets

• Level of marking can indicate how close the gun was - presence of burning/blackening from unspent powder/blackening of the blood indicates very close (1m)

Problems with gunshot residue

Similar residue to GSR may be produced by other things and activities, so can be unreliable, e.g. fireworks, care brake linings - may give false positives

GSR may be found on someone who has…

• Handled a gun

• Been near a gun being fired

• Firing range etc.

• Can be transferable from other people/objects

Problems of GSR contamination

• Suspect handled by armed officers or placed in cars with firearms or armed officers might have GSR

• Scene processor handles firearms, cartridges etc. then comes into contact with the suspect, transferring GSR

Barry George example

• Jill Dando shot dead on her doorstep from a single gunshot to the head from close range

• Barry George convicted of her murder, based on a single particle of GSR found in the pocket of his coat (difficult to get GSR on the inside of a jacket pocket)

• George appeals and questions the evidence of GSR

• GSR eventually found to be neutral and offered no evidence to support that George fired the gun

• An expert even said that it was as likely the GSR came from some extraneous source as from the gun