Time of Death, Decomposition, & Forensic Entomology

Time of Death, Decomposition, & Forensic Entomology

Forensic ScienceK. Davis

Disclaimer: This presentation contains graphic photos.

Measuring Body Temperature - Algor Mortis

• Normal Body Temperature = 98.6 ˚F (37 ˚C)• After death, the body loses heat at rate of

1.5˚F/hr until it reaches ambient temperature (T of environment).

• Rate will vary based on the environment.• Body temperature should be taken rectally or from

the liver to be most accurate.

Factors that affect algor mortis rate:

• obesity• clothing• warm still air• exposure to direct sunlight• enclosed environment

Rigor Mortis• Refers to the stiffening and contraction of

muscles caused by chemical reactions that take place in the muscle cells after death

• Begins throughout body at same time, but muscles become rigid at different rates in a predictable pattern

Predictable Pattern of Rigor Mortis1) 2 hours after death – stiffness detectable in the small

muscles of face and neck & then it progresses down toward the toes

2) Next 8 – 12 hours– entire body stiffens 3) Next 18 hours – body remains fixed

• (rigid stage of rigor mortis)

4) After the rigid stage – process reverses itself; rigidity is lost in the order that it appeared, starting with small muscles of face

5) After another 12 hours – muscles are relaxed again• (flaccid stage of rigor mortis)

• Rigor mortis is only useful for estimating time of death during first 36-48 hours after death.

Things that can alter the rate of rigor mortis:

• 1. victim who ran from assailant before death• 2. victims of strychnine poisoning• 3. victim of any fever producing process or

heat stroke• In general, heat speeds up the process and

cold slows it down.• Not always reliable to determine time of death

because the rate can be altered.

Livor mortis • Refers to dark, purplish discoloration of portions of

body• Also called lividity or postmortem hypostasis• Caused by stagnation of blood in vessels and gravity

• Usually will see lividity most wherever lowest point of body was or where body was pressed against a firm surface

• Color of lividity provides clues to ME• ex. Red or pinkish discoloration reveals high levels

of oxygen in blood which may be caused by carbon monoxide or cyanide poisoning or exposure to cold temperatures after death

• ex. Deep purple lividity may indicate death from severe heart failure, shock or asphyxia and low levels of oxygen in blood

Livor mortis

• Appears 30 minutes – 2 hrs after death• Reaches its maximum 8-12 hrs after death• Can change if body is moved in the first

few hours, but becomes fixed after 6-8 hrs• Fixing process is gradual

Livor mortis

Rate of decay• Decomposition of the body involves two

distinct processes:1) Autolysis

• process of self-ingestion• Enzymes within the body’s cells begin a

chemical breakdown of cells and tissues.• Process is hastened by heat and slowed by cold.

2) Putrefaction • Caused by bacteria that destroy body’s tissues• Bacteria mostly come from intestinal tract

Occurs in a predictable sequence:• After first 36 hours, abdomen takes on greenish discoloration

that spreads to neck, shoulders and head• Bloating begins in face, caused by gases produced by bacteria• Skin develops blisters • Skin begins to marble• Abdomen swells. Skin and hair begin to slip from body and

fingernails start to come off• Body turns greenish-black color and fluids of decomposition

drain from body• As body continues to swell, tissues break open releasing

gases and fluids

Internal organs decay in predictable manner:

• Intestines decay first, followed by liver, lungs, brain then kidneys

• Stomach decomposition is slower because of acids in stomach

• Last, uterus or prostate

V. Mummification

• Occurs when body desiccates (dries out) in a hot, dry environment

• Low humidity inhibits bacterial growth, and thus putrefaction, while at same time sucking the moisture from tissues

• Process similar to making beef-jerky• In ancient Egypt, spices and salts were rubbed on

corpses to hasten the decay

Adipocere Formation• Occurs in very wet environments within

the body’s adipose (fatty) tissues.• Fat literally turns to soap• Result is a white, greasy, waxy

substance• It gives the body an unreal,

mannequin-like appearance• Most often occurs in bodies found in

warm, damp areas• Takes at least 3-6 months to form

Floaters• Bodies that die in water or are dumped into water

shortly after death initially sink• Eventually they rise to surface because of gases that

accumulate in body’s tissues and cavities as putrefaction occurs

• Temperature of water plays a role• In general, bodies found in temperate water display

– Swollen hands and face after two to three days– Separation of skin from the body after five to six days– Loss of fingernails after 8-10 days– Floating after 8-10 days in warm water and after 2-3 weeks in

cold water

Floater

Eyes• After death, the corneas, or clear covering over the

pupils, become cloudy and opaque• Process may take only a few hours if the eyes were

open at death or up to 24 hours if the eyes were closed

• Concentration of potassium within the vitreous humor (thick, jellylike substance that fills your eyeballs) increases slowly during the first few days

• This process is independent of ambient temperature• Only really accurate though during first few days after

death

Stomach Contents• After a meal, the stomach usually empties itself in

approximately four to six hours, depending on type and amount of food ingested

• Small intestine can also be observed to see if any food remains in it

• If small intestine is empty, death probably occurred at least 24 hours after victim’s last meal

• If large intestine (colon) is also empty, no food had been ingested for 48 – 72 hours before death

• Extremely variable however, depending on individual and type of food

Entomology is the Study of Insects

Images from: www.afpmb.org/military_entomology/usarmyento/files/ArmyEntomology.ppt

Insect Biology• Insects are the most diverse and abundant forms of life on

earth.• There are over a million described species- more than 2/3

of all known organisms • There is more total biomass of insects than of humans. • Insects undergo either incomplete or complete

metamorphosis (Egg to larva to pupa to insect)• Larva have a soft tubular body and look like worms. Fly

species larvae are “maggots”

What is Forensic Entomology?

• Forensic Entomology is the use of the insects and other arthropods that feed on decaying remains to aid legal investigations. – Medicolegal (criminal)– Urban (criminal and civil)

• “legal proceedings involving insects and related animals that affect man-made structures and other aspects of the human environment”

– Stored product pests (civil)

Medicolegal Forensic Entomology

• Often focuses on violent crimes– Determination of the time (postmortem interval or PMI)

or site of human death based on identification of arthropods collected from or near corpses.

– Cases involving possible sudden death– Traffic accidents with no immediately obvious cause– Possible criminal misuse of insects

Postmortem interval (PMI)

• Forensic Entomology is used to determine time since death (the time between death and corpse discovery)

• This is called postmortem interval or PMI.• Other uses include

• movement of the corpse• manner and cause of death• association of suspects with the death scene• detection of toxins, drugs, or even the DNA of the victim

through analysis of insect larvae.

Forensic Entomology is Applied Biology • If it weren’t for decomposition of all living things, our world

would fill up with dead bodies. • When an animal dies, female insects will be attracted to the

body. They enter exposed orifices or wounds and lay eggs or larvae.

• A forensic entomologist:– identifies the immature insects– determines the size and development of the insects– calculates the growth of the insects and passage through stages of

the life cycle in laboratory– compares the growth against weather conditions to estimate time

of oviposition

Image: http://www.umext.maine.edu/images/FlyLife.jpgInformation: http://www.kathyreichs.com/entomology.htm and http://www.forensicentomologist.org/

Blow Fly Metamorphosis

1st - Adult flies lay eggs on the carcass (ex. at wound areas or around the openings in the body such as the nose, eyes, ears, anus, etc.

2nd - Eggs hatch into larva (maggots) in 12-24hrs.3rd - Larvae continue to grow and molt (shed their

exoskeletons) as they pass through the various instar stages.

1st Instar - 5 mm long after 1.8 days 2nd Instar - 10 mm long after 2.5 days 3rd Instar – 14-16 mm long after 4-5 days4th - The larvae (17 mm) develop into pupa after

burrowing in surrounding soil.5th - Adult flies emerge from pupa cases after 6-12

days.

Blow flies are attracted to dead bodies and often arrive within minutes of the death of an animal. They have a complete life cycle that consists of egg, larva, pupa, and adult stages.

It takes approximately 14-16 days from egg to adult depending on the

temperatures and humidity levels at the location of the body.

Adult

EggsPupa

3rd Instar Larva

2nd Instar Larva

1st Instar Larva

Adult

EggsPupa

3rd Instar Larva

2nd Instar Larva

1st Instar Larva

Certain circumstances can change schedule

• Blowflies for example, don’t deposit eggs at night and are less plentiful during winter

• Insect studies most often provide a minimum time that’s elapsed since death

Succession of Insects on the Corpse• Estimates of postmortem intervals based on insects

present on the remains are based on:• The time required for a given species to reach a particular

stage of development.• Comparisons of all insect species present on the remains at

the time of examination.• Ecological succession occurs as an unexploited habitat

(like a corpse) is invaded by a series of different organisms.

• The first invasion is by insect species which will alter the habitat in some form by their activities. These changes make the habitat attractive to a second wave of organisms which, in turn, alter the habitat for use by yet other organisms.

Ecology of Decomposition• Necrophages - the first species feeding on corpse

tissue. Includes rue flies (Diptera) and beetles (Coleoptera).

• Omnivores - species such as ants, wasps, and some beetles that feed on both the corpse and associated maggots. Large populations of ominvores may slow the rate of corpse’s decomposition by reducing populations of necrophagous species.

• Parasites and Predators - beetles, true flies and wasps that parasitize immature flies.

• Incidentals – pill bugs, spiders, mites, centipedes that use the corpse as an extension of their normal habitat

Image: http://www.nlm.nih.gov/visibleproofs

Decay Rates Are Variable• Studies of decay rates of 150 human corpses at in

the Anthropological Facility in Tennessee (The Body Farm)

• Most important environment factors in corpse decay: • Temperature• Access by insects• Depth of burial

• Other Factors• Chemical-- embalming agent, insecticides, lime,

etc.• Animals disrupting the corpse

Time of Death can be broadly estimated up to about 36 hours

Temperature Stiffness Time of deathWarm Not stiff Dead less than three hours

Warm Stiff Dead between 3 to 8 hours

Cold Stiff Dead between 8 to 36 hours

Cold Not stiff Dead in more than 36 hours

Differentiate between PMI and Time of Death

• These may not always equate. • Post mortem interval is restricted to the time that

the corpse or body has been exposed to an environment which would allow insect activity to begin. – Closed windows– Body in box or bag– Cold temperatures– Deeper burial

Insect species arrive at a corpse in waves like clockwork

• Calculate the heat/thermal energy (accumulated degree hour) required for each stage of the Green Bottle Fly’s life cycle.

• Possibly the greatest potential source of error in using arthropod successional patterns lies in the collection of specimens.

• Must only be done correctly to accurately sample the insects.

Image: http://www.nlm.nih.gov/visibleproofs

Calculating PMI from Accumulated Degree Hours (ADH)

From To Temp Hours

ADH Cumulative ADH

Egg 1st Instar 70° F 23 23 x 70=1610 ADH

1610

1st Instar 2nd Instar

70 ° F 27 27 x 70=1890 ADH

1610+1890

2nd Instar

3rd Instar

70 ° F 22 22 x 70=1540 ADH

1610+1890+1540

3rd Instar

Pupa 70 ° F 130 130 x 70=

9100 ADH

1610+1890+1540+9100

Pupa Adult Fly 70 ° F 143 143 x 70=

10010 ADH

1610+1890+1540+9100+10010

Calculating ADH from Climate Data

Using the Data

• 3928 ADH in these three days (952+1488+1488).

• How many ADH of 70º are there in these 3 days? 3928/70 = 56.11 hours

• 72 hours at 70º would have the insects passing to the 3rd instar. But 72 hours at colder temperatures and insects will only be at 2nd instar stage.

Five Stages of Decomposition Fueled by Insect Activity.

• Fresh• Bloat• Decay• Post-decay• Dry (skeletal)

Fresh• Begins at death• Flies begin to arrive• Temperature falls to

that of the ambient temperature.

• Autolysis, the degradation of complex protein and carbohydrate molecules, occurs.

Bloat• Swells due to

gases produced by bacteria

• Temperature rise of the corpse

• Flies still present

Decay• Gases subside,

decomposition fluids seep from body.

• Bacteria and maggots break through the skin.

• Large maggot masses and extreme amounts of fluid.

• Unpleasant odor• Larvae beginning to

pupate.• Corpse reduced to about

20% of it’s original mass.

Post-Decay• Carcass reduced to

hair, skin, and bones.

• Fly population reduced and replaced by other arthropods.

• Hide beetles are dominant in dry environments.

• Mite and predatory beetle populations increase.

Dry (Skeletal)

• Does not always occur especially if corpse is in a wet region. Maggots will stay longer and hide beetles will not appear.

• In wet environments the hide beetles are replaced with nabid and reduviid insects.

• The corpse is reduced to at least ten percent of the original mass.

• In the last stage (Skeletal Stage), only bone and hair remain.

Methods

• This project took place at the Huntington landfill beginning on September 5, 2003.

• Two different areas were chosen to deposit two pigs.– Pig 1 was laid in a sunlit area. – Pig 2 was laid in a shaded woodland area about 100 feet

away at an elevation of approximately 20 feet.• Both pigs were placed in cages constructed of wood

and one inch chicken wire that were staked to the ground to protect from predatory animals.

Methods

• Prior to starting the project, great care was taken to prevent insect activity from taking place.

• After they died, the pigs were individually tied in two black garbage bags, placed in feed sacks, and secured.

• The pigs were kept at - 80˚C in the laboratory.• They were placed in plastic bins in order to thaw for

48 hours prior to placement at the landfill.• Closed environment was maintained until they were

deposited at the site.

Methods

• Pigs with a genetic line of a minimum of fifty percent Yorkshire.

• They were 8-10 weeks old and weighed approximately 40-50 pounds.

• Both died on July 11, 2003 approximately 12 hours apart.

• One died a natural death and the other was culled from the litter.

• Both of the carcasses were in very similar condition; there were no breaks, tears or cuts in the skin.

Methods

• Daily observations were made at both sites throughout the day at 7am, 1pm, 7pm, and 1am.

• Air, ground, and maggot mass temperatures were taken at each visit and observations were recorded.

• At 7am and 7pm they also collected maggot samples for analysis and photographed the scene.

• Observations were noted and samples taken for a period of nine days.

Methods

• Using insect tweezers, the investigators collected a number of maggots and dropped the samples immediately into boiling water, to kill the bacteria in the maggots and also to straighten their bodies for easier analysis.

• The maggot samples were taken from different areas of the body in which there were large numbers present.

Methods

• The maggots were then placed into a labeled jar and preserved with 70% EtOH.

• They also collected interesting arthropods for analysis.

• All of the samples were labeled and stored for later analysis in the laboratory.

Phormia regina

Spiracles are incompleteThird-instar larvae

Phaenicia species

Spiracles are completeThird-instar larvae

Results: Fresh Stage

• Flies began to arrive within minutes of pig placement however, laying of eggs was delayed 12-18 hours.

• There was already some green discoloration on Pig 2 at the beginning of the fresh stage, possibly due to the fact that it was dead about 8 hrs before Pig 1.

• 72 hrs later, the first signs of bloating occurred, ending the Fresh Stage.

Results: Bloat stage

• At about 72 hours, noticeable bloating began to occur in Pig 1.

• However, Pig 2 did not show visible signs of bloating until about 92 hours.

• The gap between the two pigs might have been even greater if they had both died at exactly the same time.

Results: Decay Stage• Decay stage started around 102 hours. • At this point, the maggots had broken the skin and

the pigs had begun to deflate. • Decompositional fluids began to seep from the

carcass. • There was a green froth around the pig and also a

dark fluid ring around the body of Pig 1. • Maggot activity increased tremendously, and

maggot mass temperature reached its high during this stage.

Results: Post-decay Stage

• When the experiment was terminated due to the fact that maggot activity had ceased, the pigs had reached the Post-Decay Stage.

• They were mostly skin, bones, and hair, but there was some tissue remaining.

Temperature is a Factor: Pig 1

Maggot Mass and Ambient Temperatures vs Time for Pig One

05

1015202530354045

0 100 200 300

Maggot MassTemperatureAmbientTemperature

• The graph shows an elevation for maggot mass temperatures over ambient

• The fluctuation in ambient temperature induced elevated maggot activity which is consistent with other similar experiments.

Sunlit Pig

Temperature is a Factor: Pig 2

Maggot Mass and Ambient Temperatures vs. Time for Pig Two

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0 100 200 300

Maggot MassTempAmbient Temp

• The ambient temperature for Pig 2 was more constant because it was in a shaded area.

• The temperatures for Pig 1 fluctuated more than those of Pig 2.Shaded Pig

Phormia Average Maggot Length vs. Time

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2

4

6

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14

16

18

0 50 100 150 200 250

Phormia regina Pig 1Phormia regina Pig 2

• Shows a gradual increase then decrease for the Phormia regina

• The maggots feed and grow to a certain point when they begin to leave the carcass to find a safe place to pupate.

Phaenicia Average Maggot Length vs. Time

0

2

4

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8

10

12

14

16

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0 50 100 150 200 250

Phaenicia Pig 1Phaenicia Pig 2

• Two peaks for the Phaenicia

• Infers two generations for Pig 1.

Two Different Maggot Generations

• These are distinguishable

by the length and obvious size difference.

• This is why we believe there are two peaks in our graph data for the Sunlit Pig.

• The photograph was taken at a time consistent with the influx at 132 hours.

Discussion• Two different species of maggots were collected over the

nine day period.• These two species were analyzed at their third instar

stages; they were able to determine the difference by comparing their spiracles.

• The third instar was the only stage that they analyzed; species determination was more evident at this stage of development.

• They also reared a sample of maggots from each pig for later species analysis.

Accumulated Degree Hours

• ADH may be calculated using temperature and hours.

• This works because there is direct correlation between temperature and maggot development.

• These calculations were somewhat approximate but relatively accurate.

ADH and Pig Results

• ADH for Pig 1 was calculated as 4885.2 after nine days.

• ADH for Pig 2 was calculated as 4488.6 after nine days.

• These can be used to determine PMI for carcasses found in this area in similar conditions.