Now that you know what weapons are made of, let’s further investigate how they work from a chemical perspective.
The Gun
Guns are dangerous because they fire projectiles at a high rate of speed that cause cellular damage when they strike the body. So first, how do they fire and second how do they cause death? We know these things in general but let's look at the specifics.
We learned in an earlier lecture about black or gun powder. It is actually a slow burning accelerant that forms gases as it burns. If those gases are contained in a cylinder they will accumulate until they burst the cylinder.
Bullets are cylinders that contain a packing of black powder and a primer to create a spark to start the reaction. Once the reaction begins, the gases that are produced build up rapidly and then eject the projectile from the front of the bullet. The part of the bullet left behind is called the cartridge.
The projectile is fired at a rate of 120 m/s to 1700 m/s depending on the type of gun and powder used. The rate at which a projectile leaves a gun is called its Muzzle Velocity.
At the other end of the firing of a bullet is the poor fellow that gets hit with the projectile. The wound that is received is called ballistic trauma.
Ballistic Trauma
The degree of tissue disruption caused by a projectile is related to the size of the cavity it creates as it passes through the body. The extent of cavitation (the hole it makes) is related to the following characteristics of the projectile:
- The kinetic energy (KE) of the bullet (KE = ½(mass)(velocity)2)
- The Yaw (spinning movement)
- Deformation (how flattened or squashed it is)
- Fragmentation (how many pieces it breaks into)
Generally, the faster the bullet travels or the larger it is, the greater the damage. Once the bullet strikes the body the primary cause of death is blood loss, the secondary cause is shock.
The Knife
A knife is a sharpened piece of metal or wood or other hard material that caused punctures or cuts when used on soft tissue. Knife wounds have distinct structures that can be used for comparison based on the type of knife used.
Stab wounds are incised wounds where the length of injury on the surface is less than the depth of penetration into the body, and are the result of a thrusting action, where the force is delivered along the long axis of a narrow, pointed object. The force of impact is concentrated at the tip of the implement, and the sharper the tip, the easier it will penetrate the skin.
Characteristics of stab wounds:
- Clean cut edges
- Often gape open
- Cross section of weapon may be illustrated when edges of wounds are examined
- Underlying bone may be scored by blade
- Abrasions may be present
- Frequently shows notching or a change in direction (caused by relative movement of the knife and body)
The cause of death from stab wounds is the same as that for bullet wounds: blood loss and shock.
The Bat
The use of a bat or club to kill is not as common as the use of a gun or knife but is still a method worthy of study. The trauma induced by a bat is called "blunt force trauma" because there are generally no sharp edges or puncture wounds produced with the use of a bat.
The cause of death from blunt force trauma is normally internal hemorrhaging (bleeding). This too is blood loss but because of the lack of a puncture wound the blood stays internal and is seen visually as bruising.
When a bat or club is used to kill, the head is the primary target. The wounds to the skull can be both coup and contrecoup as the primary impact causes the head to rebound and strike another surface.
The brain can be injured by blunt force trauma in two ways:
- Damage to the Cerebral Cortex causing brain death. Nerves are damaged and normal brain activity ceases.
- Damage to the Cranium causing a piece of bone to enter the brain.
The Ligature
The ligature is used to cut off the air supply to the victim. This is defined as Ligature Strangulation. The ligature is pulled tight against the throat and neck of the victim in a U-shape.
Upon sudden and violent compression of the neck, the victim is very quickly rendered unconscious and if pressure is maintained death soon follows. The process of death is violent with convulsions, bleeding from the mouth, nose and ears possible.
Garrote – Handled Ligature
Death is caused by asphyxia or cerebral anoxia. Asphyxia is when the body is deprived of oxygen causing hypoxia. Hypoxia is oxidative stress that causes a reaction in the body through several signal pathways that can eventually lead to cellular apoptosis. Apoptosis is cell death. The apoptosis results in cells rupturing and internal bleeding especially in the brain. Cerebral anoxia is the total cutting off of oxygen to the brain. The lack of oxygen induces the same processes we learned about in the lecture on time of death.