forensic science forensic biology time of death. forensic file #1 what are 2 important things that...
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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
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?
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
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