Forensics
Death: Manner, Mechanism & Cause
- Purpose of bell (19th Century England): Prevent premature burial by alerting someone if buried alive.
- PMI (Postmortem Interval): Time elapsed since death; helps reconstruct timeline of death.
- Coroner/Medical Examiner Called: When death involves suspicious circumstances, unknown cause, unnatural death.
- Pathologist: Trained forensic specialist examining bodies to determine cause and manner of death.
Manners of Death (HOW they died):
1. Natural: Body failure due to age, disease, toxins.
2. Accidental: Unplanned events (car crash, fall).
3. Suicidal: Self-inflicted death.
4. Homicidal: Death caused by another person.
5. Undetermined: Cannot clearly categorize.
Definitions:
- Cause of Death: Reason person died (injury, disease, poisoning, heart attack).
- Mechanism of Death: Specific body change causing death (cardiac arrest from heart attack).
The Process of Death:
- Death: Occurs when vital organs (heart/brain) cease functioning.
- Stage 1 (Stoppage):
- Heart stops, blood flow stops, no oxygen or glucose to cells.
- Anaerobic respiration, lactic acid builds up, cells rupture.
- Stage 2 (Autolysis - Cell Self-Digestion):
- Cellular enzymes destroy cells after death.
Algor Mortis (Body Cooling):
- Cooling towards ambient (surrounding) temperature.
- Body temperature taken in liver/rectum.
- Cooling Rates:
- 1st 12 hours: ~1.4°F/hr.
- After 12 hrs: ~0.7°F/hr until ambient temp.
- Heat Loss Factors:
- Thin bodies cool faster than heavy ones.
- Extended body cools faster than curled-up body.
- Clothing, fluid retention, colder environment, windy/submerged bodies affect cooling rate.
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Livor Mortis (Blood Pooling):
- Blood settles due to gravity.
- Lividity: Reddish-purple discoloration.
- Appears ~2 hours after death; permanent after 8 hours.
- Influencing Factors: Temperature, anemia, blood loss.
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### Rigor Mortis (Death Stiffness):
- Temporary muscle stiffness.
- Begins ~2 hours after death, progresses small to larger muscles, peaks ~12 hrs, disappears after 36-48 hrs.
- Factors: Temperature, body mass, age, clothing.
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Stages of Decomposition:
- Influenced by age, size, illness, environment, clothing.
- Decomposition Timeline:
1. Few hours: Cell autolysis, muscle tone loss, flies lay eggs.
2. Several days: Increased insect activity, blistering, putrefaction begins.
3. 7–23 days: Discoloration, bloating, skin rupture.
4. 3 weeks–2 months: Advanced decay, tissues breaking down.
5. 2+ months: Bones primarily remain.
- Putrefaction: Decay or rotting due to bacteria and enzyme activity.
- Around body: Flies, bloating, skin ruptures, odors.
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Autopsy:
- Definition: Medical examination determining manner/cause of death.
- Performed by forensic pathologist.
- Mandatory for suspicious deaths (injury, poisoning, infections, foul play).
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Forensic Entomology:
- Entomology: Study of insects; used in forensic investigations.
- Uses insect evidence (type, stage, location) to estimate PMI.
- Reveals PMI, crime scene location, body movements, abuse, exposure to toxins, suspect/victim identity, drug origin.
Decomposition & Insects:
- Stages:
1. Fresh: Warm, newly dead.
2. Bloated: Odor, fluid seepage.
3. Active Decay: Strong odors, darkened tissues.
4. Advanced Decay: Drying out, most flesh gone.
5. Dry/Skeletal: Primarily bones.
- Blowflies:
- Detect decomposition gases from 1 mile away, lay eggs (oviposition) in body openings/wounds.
- Larvae feed on body fluids and tissues.
- Carrion Beetles: Feed on eggs/larvae of flies.
Blowfly Life Cycle:
- Eggs → hatch quickly into larvae.
- Larvae (maggots) → feed on tissues.
- Pupae → larvae form cocoons.
- Adult flies emerge from pupae.
Larva Morphology:
- Anterior (front): Slender, tapered with hooks for scraping flesh.
- Posterior (rear): Rounded, breathing spiracles (slits).
- Crop: Larva’s food storage organ.
Factors Affecting PMI Estimation (Insects):
- Temperature, humidity, rainfall, sunlight/shade, location, presence of wounds, and toxins.
- DNA Retrieval (Badly Burned/Decomposed Bodies):
- Obtained from larvae feeding on victim.