Forensic Science Forensic Biology - PowerPoint Presentation

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Forensic Science

Forensic Biology

Time of Death

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What happens once a body is found?

Medical examiner or coroner must pronounce the person “dead”

Photographs are taken of body “in situ”- in position found

Any physical evidence around body is photographed and collected

Body may be rearranged, clothes searched for ID, some evidence obtained at scene (skin swabs for trace evidence)

Medical examiner may try to determine manner of death at scene- to determine if body needs to be taken to the morgue or if it can be released to funeral home

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Identify manner, cause, mechanism of death

Manner of death: Accident, homicide, natural, suicide, undetermined

Cause of death: bleeding out, heart failure, brain death, asphyxiation

Mechanism of death: what causes the “cause”

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Example:

A man dies from a stab wound to the abdomen that he obtained during a fight with another person.

Manner- homicide

Cause- bleeding out

Mechanism- knife wound

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Determination of time of death

Time of death is important to investigators because it can establish when crime occurred- check alibis of suspects, know when to question witnesses, etc.

Utilize:

livor

mortis, rigor mortis,

algor

mortis and insect activity to determine time of death or PMI (post mortem interval)

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What is

livor

mortis?

Means “death color”

Blood pools at the lowest point of the body once heart stops beating

Lividity

begins about 2 hours after death

Discoloration becomes permanent after 8 hours

Influenced by temperature- faster when warmer

Discoloration is on back of body- indicates body was face up

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What is rigor mortis?

Means “death stiffness”

Starts within

2 hours

of death

Starts with head & moves down body

Stiffness occurs because the skeletal muscles are unable to relax and remain contracted & hard

These changes occur due to chemical changes that occur after death

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What affects rigor?

Ambient temperature

Person’s weight

Type of clothing

Illness

Level of physical activity prior to death

Sun exposure

Essentially- the warmer the person was at death, faster rigor occurs

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Progression of Rigor

Time after death

Event

Appearance

Circumstances

2 to 6 hours

Rigor begins

Body becomes stiff & stiffness moves down body

Begins with eyelids & jaw, then center, then extremities

12 hours

Rigor complete

Peak rigor is exhibited

Entire body is rigid

15 to 36 hours

Slow loss of rigor

Loss of rigor in small muscles first then large

Lost first in head & neck; last in bigger leg muscles

36 to 48 hours

Rigor totally disappears

Muscles become relaxed

Many variables may extend rigor

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What is algor mortis?

Means “death heat”

Describes temperature loss that occurs after death

Temperature taken with thermometer inserted into the liver to get a “core temperature”

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Today’s assignments

Today’s assignment: Time of Death packet on front table

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Time of Death-

Day Two

Make sure your name is on your Time of Death

packet and turn it in



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Checking for Understanding

This body was found at the scene face down and the lead investigator immediately knew that the body had been moved. How did he know?

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Other methods to determine time of death

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Why look at stomach and intestinal contents?

4 to 6 hours for the stomach to empty its contents

Another 12 hours for food to leave small intestine

takes approximately 24 hours after the meal until undigested food is released

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What changes in the eye after death?

Surface of eye dries out

Thin film is observed within 2 to 3 hours after death

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What are the stages of decomposition?

After 2 days: cell autolysis; green/purplish staining; skin marbles; face becomes discolored

After 4 days: skin blisters; abdomen swells

Within 6 to 10 days: corpse bloats/splits; fluids begin to leak; eyeballs/tissues liquefy; skin sloughs off

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Stages of decomposition

Stage

What happens

Initial decay

Normal on outside; starting to decompose

Putrefaction

Odor of decay present; corpse swollen

Black putrefaction

Very strong odor; flesh appears black; gases escape & corpse collapses

Butyric fermentation

Corpse is beginning to dry out; most of flesh is gone

Dry decay

Corpse is almost dry

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Evidence of physical trauma

Appearance and extent of injuries depend on:

Amount of force

Weapon’s surface area and mass

Part of body affected

Force= mass x acceleration

Pressure= force/surface area

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Types of trauma

Blunt-force trauma- victim is hit by something hard, or falls onto a hard object

Blunt force trauma is divided into three categories:

Abrasions

Contusions

lacerations

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Abrasions

When portion of the skin has been removed

Brush abrasions- force applied parallel to skin (brush, scrape) skin damaged in direction of the force

Impact abrasions- force applied perpendicular to the

skin

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Contusions

Also known as a bruise

Trauma caused by broken blood vessels

May be large enough to cause swelling- hematoma

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Laceration

Tear in the tissue caused by sliding or crushing force

Extreme force involved

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Sharp-force trauma

Four categories

Stab wounds

Incised wounds

Chop wounds

Therapeutic wounds

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Stab wounds

Typically deeper than it is wide

Penetrating wounds- result in punctured organs

Perforating wounds- puncture an organ and come out the other side

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Incised wounds

Longer than it is deep

Usually center is deepest

Not typically fatal

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Chop wounds

Heavy tools

Incised wounds with deep internal injuries

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Therapeutic wound

Produced by surgery

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Today’s agenda:

Due today- Time of death packet

Today’s work: BOTH

on front table

Diagramming injuries

Applying directional terms