Forensic Science

Forensic BiologyTime of Death

Forensic File #1

What are 2 important things that microorganisms like diatoms, algae, and/or other protists can tell a forensic scientist?

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

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”

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

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)

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

What is rigor mortis?

Means “death stiffness” Starts within 2hours 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

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

Progression of RigorTime 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

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”

Today’s assignments

Due today: Microbe Murder Mystery lab

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

Time of Death-

Day Two

Make sure your name is on your Time of Death packet

Forensic File #2

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?

Other methods to determine time of death

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

What changes in the eye after death? Surface of eye dries out Thin film is observed within 2 to 3

hours after death

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

Stages of decompositionStage 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

Evidence of physical trauma

Appearance and extent of injuries depend on:

1. Amount of force2. Weapon’s surface area and mass3. Part of body affectedForce= mass x accelerationPressure= force/surface area

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:

1. Abrasions2. Contusions3. lacerations

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

Contusions

Also known as a bruise Trauma caused by

broken blood vessels May be large enough

to cause swelling- hematoma

Laceration

Tear in the tissue caused by sliding or crushing force

Extreme force involved

Sharp-force trauma

Four categories1. Stab wounds2. Incised wounds3. Chop wounds4. Therapeutic wounds

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

Incised wounds

Longer than it is deep Usually center is deepest Not typically fatal

Chop wounds

Heavy tools Incised wounds with deep internal

injuries

Therapeutic wound

Produced by surgery

Today’s agenda:

Due today- Time of death packet

Today’s work: BOTH on front table Diagramming injuries Applying directional terms