Time of Death, Decomposition, and Forensic Entomology Forensic Science K. Davis.

Time of Death, Decomposition, and Forensic EntomologyForensic ScienceK. Davis

I. 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:1. obesity2. clothing3. warm still air4. exposure to direct sunlight5. enclosed environment

II. 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.

III. 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

•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

IV. 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 Process is hastened by heat and slowed by cold

Decomposition of a pig

•Occurs in a predictable sequence:1) After first 36 hours, the abdomen takes on greenish

discoloration that spreads to neck, shoulders, and head.2) Bloating begins in the face; caused by gases produced by

bacteria3) Skin develops blisters or accumulations of fluid4) Skin begins to marble5) Abdomen swells. 6) Skin and hair begin to slip from body, and fingernails start

to come off. 7) Body turns greenish-black color and fluids of decomposition

drain from body8) As the body continues to swell, tissues break open releasing

gases and fluids.

• Internal organs decay in predictable manner:

1) Intestines decay first, followed by liver, lungs, brain then kidneys

2) Stomach decomposition is slower because of acids in stomach

3) 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

VI. 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

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

shortly after death initially sink.•Eventually, they rise to the surface because of gases

that accumulate in body’s tissues and cavities as putrefaction occurs.

•The temperature of the water plays a role.•Display:

▫Swollen hands and face after 2-3 days▫Separation of skin from the body after 5-6 days▫Loss of fingernails after 8-10 days▫Floating after 8-10 days in warm water and 2-3 weeks in

cold water

Floater

VIII. 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

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

approximately 4-6 hours, depending on type of food ingested.

•The small intestine can also be observed for remaining food.

• 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.

•This is extremely variable however, depending on individual and type of food.

X. Forensic EntomologistsThey apply their knowledge of entomology to provide information for criminal investigations.A forensic entomologist’s job may include:• Identification of insects at various stages of their life cycle, such

as eggs, larva, and adults.• Collection and preservation of insects as evidence.• Determining an estimate for the postmortem interval or PMI (the

time between death and the discovery of the body) using factors such as insect evidence, weather conditions, location and condition of the body, etc.• Testifying in court to explain insect-related evidence found at a

crime scene. Did you know? Maggots can be used to test a corpse for the presence of poisons or drugs. Some drugs can speed up or slow down the insect’s development.

Cool Jobs: Forensic Entomology

Discovery Video

Insects as EvidenceForensic entomologists use their knowledge of insects and their life cycles and behaviors to give them clues about a crime. Most insects used in investigations are in two major orders:

1 – Flies (Diptera) and2 – Beetles (Coleoptera)

Blow Fly

Carrion Beetle

Images: Top Right - http://www.insectinvestigations.com/aboutfe.htm, Chart - http://www.clt.uwa.edu.au/__data/page/112507/fse07_forensic_entomology.pdf

Species succession may also provide clues for investigators. Some species may to feed on a fresh corpse, while another species may prefer to feed on one that has been dead for two weeks. Investigators will also find other insect species that prey on the insects feeding on the corpse.

Weather data is also an important tool in analyzing insect evidence from a corpse. Investigators will make note of the temperature of the air, ground surface, the interface area between the body and the ground, and the soil under the body as well as the temperature inside any maggot masses. They will also collect weather data related to daily temperature (highs/lows) and precipitation for a period of time before the body was discovered to the time the insect evidence was collected. Other factors that might affect their PMI estimates:1. Was the body enclosed in an area or wrapped in a material that would have prevented

flies from finding the corpse and laying eggs?2. Were other insect species present that may have affected the development of the

collected species?3. Were there drugs or other poisons in or on the body that might have affected the larvae’s

development? http://video.nationalgeographic.com/video/science/health-human-body-sci/human-body/body-farm-sci/

Did you know…The “Body Farm” in Knoxville, Tennessee is a university research facility to investigate human decomposition under various conditions in order to understand the factors which affect its rate. Click the image to view a

video about the Body Farm!

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 has elapsed since death.

Examples of Diptera (Flies)

Informational Source: http://naturalsciences.org/files/documents/csi_tg_overview.docImages: Top Left - http://www.scienceinschool.org/repository/images/issue2forensic3_large.jpg, Middle-Left: http://forensicfact.files.wordpress.com/2008/04/blowfly053.jpg, Top Right - http://users.usachoice.net/~swb/forensics/P1.jpg, Bottom - http://www.deathonline.net/decomposition/corpse_fauna/flies/index.htm

Flesh Fly(Sarcophagidae)

Striped thorax

Blow & Greenbottle Flies(Calliphoridae)

Metallic thorax and abdomen

House Fly(Muscidae)

Cheese Skipper (Piophilidae)

Early Stage Decomposition

Late Stage Decomposition

Life Cycle of a Calliphoridae Fly

Examples of Coleoptera (Beetles)

Informational Source: http://naturalsciences.org/files/documents/csi_tg_overview.doc Images: http://www.cals.ncsu.edu/course/ent425/library/spotid/coleoptera/coleoptera.html & http://www.forensicflies.com/beetles.htm

Carrion Beetles (Silphidae)Adults & larvae feed on fly larvae

Early to Late Stage Decomposition

Late Stage Decomposition

Rove Beetles (Staphylinidae)

Predator of fly eggs

Early Stage Decomposition

Hide Beetles (Scarabidae)

Usually the last to arrive

Clown Beetles (Histeridae)

Predator of fly eggs

Ham & Checkered Beetles (Cleridae)

Predator of flies & beetles; also feed on dead tissue Skin Beetles (Dermestidae)

Feed on dried skin & tissues

Click the image above or click here to visit the website at http://www.pbs.org/wnet/nature/episodes/crime-scene-creatures/interactive-determine-the-time-of-death/4390/

Let’s give it a try …

XI. Scene Markers•ME will use all information available to

determine time of death, including many non-scientific findings.

•Examples▫Broken watch or clock▫Victim who missed work for 2 days and is

found near his or her front door, dressed in work attire, and holding car keys, probably was heading to work at time of death.