HOSA Forensic Science - Crime Scene and Death Investigation

Some examples of defining a crime scene include...

- Location (primary, secondary)

- Size (macroscopic, microscopic)

- Type of crime

- Condition

- Physical location

- Type of criminal behaviour

What is the objective of processing a crime scene?

Recognize, preserve, collect, and interpret all physical evidence at a scene

Locard's Exchange Principle

Whenever two objects come into contact there will be a mutual exchange of matter between them

5 Crime scene investigation models

1. Traditional

2. Crime scene technicians

3. Major crime squad

4. Lab crime scene scientist

5. Collaborative team

List the steps taken by the First Responding Officer

1. Assist the victim

2. Search for and arrest suspect if on scene

3. Detain witnesses, and keep separate

4. Secure crime scene

5. Establish crime scene security log, recording any persons entering/exiting

List the steps of a Crime Scene Survey

1. Perform survey/walkthrough

2. Note any evidence present requiring immediate protection/processing

3. Be aware of weather conditions

4. Not points of entry/exit or paths of travel w/in scene

5. Document scene's condition before processing

4 Major tasks of documentation

1. Note taking

2. Videography

3. Photography

4. Sketching

Cause of death

The disease or injury that initiated the lethal chain of events, either brief or prolonged, that led to death

Mechanism of death

The biochemical or physiological abnormality produced by the cause of death that is incompatible with life

True or false? Injury takes precedence over disease in determining cause of death

True

Manner of death

The fashion in which the cause of death came to be

5 Manners of death

1. Natural

2. Accidental

3. Homicidal

4. Suicidal

5. Undetermined

Livor Mortis

Discolouration of the body that occurs from the settling of red blood cells after the blood stops circulating; can be seen minutes after death; slowly disappears w/ decomposition after 36 hours

Algor Mortis

Cooling of the body after death assuming the ambient temp is lower than body temp

Rigor Mortis

Stiffening of the muscles that occurs ~4 hours following death; chemical rxn when glycogen normally found in muscles is not reformed; generally disappears 24-36h after death

Tools of death investigation

1. Reviewing medical history

2. Reviewing witness statements

3. Scene examination

Inframammary incision

Beginning at each shoulder, extending to the midline of the body in the lower chest, and extended to the top of the pubic bone (T-shaped incision)

Examination of the brain

An incision is made from behind one ear to behind the other, reflection of the scalp by peeling it upward and backwards then sawing the skulls in a circular cut followed by removing the skull cap

Classifications of traumatic deaths

1. Mechanical

- Sharp force

- Blunt force

- Non-firearm

- Firearm

2. Thermal

3. Chemical

4. Electrical

What is mechanical trauma?

An applied physical force that exceeds the tensile strength of the tissue

How are incised wounds produced?

By sharp objects during mechanical trauma

How are lacerations produced?

By blunt objects during mechanical trauma

What is the most common cause of death from mechanical trauma?

Exsanguination or bleeding to death

What is the most common cause of death in cases of Mechanical Trauma?

Significant brain damage

How can Mechanical Trauma from blunt force lead to death?

Laceration of the heart or aorta causing exsanguination

How does the velocity of a projectile affect the type of injury in Mechanical Trauma?

The velocity of the projectile determines how the injury is produced

What differentiates a Penetrating gunshot wound from a Perforating gunshot wound?

Penetrating wounds have an entrance wound only, while Perforating wounds have both entrance and exit wounds

What is the significance of finding no exit wound in a gunshot wound during autopsy?

The projectile must be recovered during autopsy

Mechanical Trauma - Firearms

- When a firearm discharges, the bullet is ejected from the barrel along with hot expanding gases, unburned propellant, and other residues

- How far each component travels can be used as an estimate for determining the distance of the barrel from the deceased at the time the weapon was discharged

- Unburned powder produces stippling or tattooing around the bullet hole

- Distant gunshot wounds lack the effects from smoke and powder

- Typical wound will have a circular skin defect with a rim of scraped skin around the edges

- Diameter of the skin defect is some indication of the diameter of the bullet but is not reliable

- Exit wounds are typically lacerated

Skin will show variable amounts of laceration due to ____ blown into the wound that tears it apart

Gas

How are gases from firearms seen in the victim?

Blackening of the skin

Carbon monoxide reacts with what to produce carboxyhemoglobin and carboxymyoglobin

Hemoglobin and myoglobin

As the distance from the barrel _________, the effect of the gas __________ and only unburned powder and bullet penetrate the skin

Increases, decreases OR decreases, increases

When is mechanical trauma by blunt force trauma most common other than in firearms?

Motor vehicle collisions

Generally, homicidal blunt trauma in adults requires lethal ____ injuries

Head

True or False? Blunt force trauma to the head leads to copious bleeding.

True, due to the vascularity of the scalp

What is the most common mechanism of death from blunt force trauma?

Drowning in the blood that has aspirated into the lungs

Contusion

An accumulation of blood in the tissues outside the blood vessels

Hematoma

Blood tumor is a contusion with more blood

Chemical Trauma

Deaths that result from use of drugs and poisons

Central nervous system depressants

Increasing degrees of coma followed by cessation of breathing and subsequent death

Ex. Alcohol, Barbiturates, Benzodiazepines, Opiates

Central nervous system stimulants

Results in seizures, extremely high body temp, and uncontrolled quivering of the heart

Ex. Cocaine

Carbon monoxide

Odourless, colourless, explosive gas produced by the incomplete combustion of carbon-containing fuels

Ventricular fibrillation

Caused by low voltage, a quivering of the heart that leads to non-resuscitability

Defibrillation

Caused by high voltage, and forces the heart into tetany

Tetany

A sustained contraction that is broken when the circuit is broken

Poration

Holes in the membranes of cells in tissues caused by the flow of electrical current