Unit 8 Time of Death

Rigor Mortis

"Death stiffness"-Stiffness occurs because the skeletal muscles are unable to relax. Temporary and begins within 2 hours of death. After 12 hours the body is mostly rigid (full rigor). Ends after 36-48 hours. A body is in rigor mortis when the head and neck muscles are stiff, but the rest of the body is not

The Rigidity of Death

(Stiffness of the body) Without oxygen in the blood— 1.) Calcium accumulates in the muscles 2.) Muscles stiffen (Starts in the head and expands throughout) 3.) After about 15 hours— -Muscle fibers begin to dissolve -Softening begins

Fresh

-Immediately after death -Lividity begins -Rigor mortis may begin -Body temperate begins to acclimate to the environment -Cells will begin to break down and release enzymes which can cause blisters on the skin -The anaerobic organisms in the digestive tract will begin to multiply, producing acids and gases (the source of the bad odors)

How do different seasons affect determining then PMI of a body?

-Some fly species are active in the early spring, different species are active in the fall, and others are continuously active. -If an insect larvae which is more abundant in the fall is discovered, this can indicate the body was undiscovered for many months, while if larvae are found from spring flies, this could indicate the cadaver is more recent, or that it was recently exposed to the newly emerged adult flies.

Bloated (decay)

-The gases begin to build and will give the body a distended appearance -Gases and fluid will eventually escape through the natural orifices as the pressure builds. -Gastrointestinal bacteria multiply and can lead to a discoloration pattern seen in the skin

What are the different time periods at which body stiffness occurs?

0-2 hours: no visible signs of rigor 2-15 hours: body is at its most rigid state 15-36 hours hours: body very gradually becomes less stiff 36-48 hours: stiffness generally disappears After 48 hours: no visible signs of rigor

What are some factors that affect the timing of rigor mortis?

1. Ambient temperature 2. Weight of the body 3. Type of clothing, or lack of it 4. General health of person at time of death 5. Level of physical activity at time of death 6. Sun exposure

What are the two families of carrion flies?

1.) Blow flies (calliphoridae) -Iridescent blue, green, copper, or black bodies. 2.) Flesh flies (sarcophagidae) -Grayish, usually with three distinct longitudinal dark stripes on the dorsal thorax.

What is the life cycle of flies?

1.) Eggs: -The adult female fly lays her eggs on the exposed tissue within minutes of death. -The eggs hatch within approximately 24 hours of being laid. 2.) First Instar: a stage of maggot larvae -Crawl to the closest food source and begin to eat (simply just eat and grow rapidly) -Will double in size over the next 27 hours 3.) Second Instar: -Maggots shed their old skin and convert into second instars -Continue to eat and grow until shedding after 22 more hours 4.) Third Instar: two parts that last 100 hours in total -Feeding third instar: continue to eat and grow -Migrating third instar: stop eating and move away from their food source 5.) Pupae: -Enclose themselves in a hard shell and begin metamorphosis (pupae) 6.) Adult: -Convert into an adult eventually

What is the PMI if the body is warm and there's stiffness present in the middle extremities and medium muscles only?

3-8 hours

What is the PMI if the body is cold and stiffness is present throughout the body?

8-36 hours

Speed of decomposition depends on...

A person's size of the body and nature of death Sick individuals decompose faster than elderly-more moisture faster decay Overweight faster than people of normal weight Naked bodies decompose faster than clothed bodies-exposed to elements Extremely high temperatures dry out corpses, preserving them Colder temperatures prevent bacterial growth and slow decomposition

Mechanism of death

A specific change in the body that stopped life (Ex-Cessation of brain function, pulmonary arrest, loss of blood, exsanguination)

Autopsy

Also called a post mortem examination, is ma examination of a person's body and organs after death uses a Y-cut to cut open the torso

Proximate cause of death

An underlying cause of death (radiation, exposure)

What stage of decomposition are carrion flies attracted to?

Bloated corpse: -Therefore they will only be present on a corpse once that stage is reached.

Insect arrival sequence

Blowflies→ tiny wasps (attracted to seeping fluid) → mites and beetles (favor drier conditions)

What is the significance of forensic entomology?

By inspecting the corpse, time of death can be estimated - can determine if the body has been at a site for many hours or several days (estimate time of death) -Within minutes of a death, certain insects arrive to lay their eggs on the warm body—blowflies - attracted to smell of 1st stage of decomposition (takes place at surprisingly consistent time intervals)

What are the four stages of decomposition?

Cadavers decompose in four stages: fresh, bloated, active decay, and dry decay.

Carrion

Carcasses: Dead and rotting flesh -Some fly species specialize in living on carrion (are the most important insects to the forensic entomologist) -What drives forensic entomology (what makes it so useful)

What is the proper definition of death?

Cessation, or end of life: -Irreversible cessation of blood circulation -Cessation of all brain activity -Experts do not agree on a single definition

What are the five manners of death?

Classification of death: 1. Natural, the most common 2. Suicidal 3. Homicidal 4. Accidental 5. Undetermined -Sometimes the manner of death is difficult to determine

Dry decay

Corpse is almost completely dry, further decay is slow due to a lack of moisture

How is corpse temperature measured?

Corpse temperature is measured by a thermometer inserted into the liver

Where to look for bugs

Data includes the environmental conditions (temperature, moisture, wind) around the body as well as below it-Insects are attracted to gases (putrescine and cadaverine)

If there is undigested contents in the stomach...

Death occurred about 2 hours after the last meal

If the small intestine is empty and wastes are found in the large intestine...

Death occurred at least 12 or more hours after the meal

If the stomach is empty but there is food in the small intestine...

Death occurred at least 4-6 hours after the meals

Ambient temperature

Determines the temperature of the immediate surroundings

Cause of Death

Event that directly caused death (reason for the death) -Heart attack, bleeding to death from wound

Characteristics of larva (the maggot stage)

First instar-(1.8 days)-V shaped slit Second instar-(2.5 days)-2 slits Third instar-(4-5 days)-3 slits

What stage of decomposition are adult blowflies attracted to?

Fresh corpse: -Will lay their eggs at this stage

Dual lividity

If the body was kept in one position 2 hours after death then moved to a second position before lividity became permanent

Factors affecting heat loss

If the temperature is cool heat loss occurs faster Wind increases the rate of heat loss Excess body fat slows heat loss Presence of clothing slows heat loss

What is the PMI if the body is warm and there's stiffness present in far extremities and small muscles only?

Less than 3 hours

Livor Mortis

Livor Mortis-"death color"-The settling of blood to the lowest parts of the body

Why is it impossible to determine the exact moment of death?

Many different people have different versions of what death is. Some people say that a person has died when there is no brain activity, and other says that the moment of death occurs when blood circulation stops within the body.

What factors affect a body's decay?

Most important environment factors in corpse decay: 1. Temperature 2. Access by insects 3. Depth of burial Other Factors: 1. Chemical-- embalming agent, insecticides, lime, etc. 2. Animals disrupting the corpse

Can the study forensic entomology provide an exact time of death of an individual?

No: -The insect life cycle provides scientists with a benchmark to estimate a time of death -Insect evidence cannot provide an exact time of death due to fluctuating environmental conditions

What is the PMI if the body is cold and there is no stiffness present?

Over 36 hours

Lividity

Pooling of blood in the body-Begins about 2 hours after death, permanent after 8 hours-Affected by temp, environmental conditions, anything impeding blood flow

Mechanism of Death

Specific change in the body that brought about the cessation of life

Entomology

Study of insects

Forensic Entomologist

Study presence of insects on corpses: -Collects insect evidence from on, above, and below the body -Records environmental conditions -Provides data used to estimate the time that elapsed between the actual death and when the body was first discovered.

Factors affecting insect development

Temperature, moisture, wind, time of day, season, exposure to the elements and variations among individual insects

How does the temperature of the body change after the body is considered deceased?

The Chill of Death: -Body heat falls after death (About 1.5 degrees per hour immediately after death) -Slowing to less than 1.0 degree per hour after about 12 hours -Heat loss is affected by the ambient temperature

Active Decay

The body begins to lose much of it's fluids and mass (tissue) through purge and insect and/or vertebrate scavenging -May see very large maggot masses and notice a considerable increase in foul odors

Autolysis

The breakdown of cells

Death

The cessation (end) of life-has 2 stages 1) When the heart stops beating 2) Autolysis

Why is the development rate of a corpse measured in degree-hours?

The development rate is VERY temperature dependent. -If an egg takes 23 hours to develop into the 1st instar at 70 ̊F, then 1610 degree-hours would have accumulated. Temperature x Development Hours = degree hours

Oviposition

The laying of the eggs-If there is presence of blowfly eggs, time of death is 24 hours or less

Manner of death

The means by which someone dies (natural, accidental, suicidal, homicidal, undetermined)

Succession

The ordered series of insects attracted to the decomposing body -The succession pattern is useful in estimating how long a cadaver has been exposed to the insects.

Decomposition

The rotting of all tissues and organs

The Post Mortem Interval

The time that has elapsed since a person has died: -Recent PMI (0-50 hours) is estimated by a medical examiner or forensic pathologist based on physical changes to the cadaver. -If a body remains exposed to the environment for a longer period of time, the normal physical changes observed after death may not provide an accurate PMI estimate.

What affects the time that the corpse spends in a stage of decomposition?

The time the body spends in any individual stage will vary depending on environmental conditions: -Warm, wet weather speeds decay -Cold, dry weather slows it.

Overall, what is the main contrast between time of death and PMI?

Time of death: when the person died PMI: restricted to the time that the corpse or body has been exposed to an environment which would allow insect activity to begin. This could be affected by factors such as: 1. Closed windows 2. Body in box or bag 3. Cold temperatures 4. Deeper burial

Succession Databases

When a crime scene is investigated, the forensic entomologist compares the insect species and their distribution of larval stages to the database to estimate the time of death. -For storing and retrieving data when needed

What happens to a corpse's stomach and intestinal contents after death?

Zero to two hours after the last meal: undigested food is still present in the stomach Death occurred four to six hours after the last meal: stomach is empty, but food is found in the small intestine Death occurred 12 or more hours after a meal: Small intestine is empty; waste found in large intestine

Algor mortis

postmortem cooling of the body to the surrounding temperature