Forensic science chap 5 part 2

Explain how insect development can serve to approximate TOD

Insects that feed on dead tissue are the first to infest the body, usually within 24 hours.

• How it works: Insects, especially blowflies, colonize a body in a predictable sequence. Its life cycle and many stages happens at a known time interval that span over about a month. By identifying the most mature insect stage (egg, 1st instar larva, 2nd instar, 3rd instar, pupa, adult) on the body, a forensic entomologist can estimate the Postmortem Interval (PMI- this is the time that has elapsed since death)

This method is highly effective for estimating TOD from hours to approximately one month, especially when other methods like algor and rigor mortis are no longer relevant.

what are the stages of decomposition?

After death, two decomposition processes take place: autolysis and putrefaction. Autolysis is the self-digestion of cells by their own enzymes. Putrefaction is accompanied by bloating, discoloration and a foul smell caused by acummulating gases. In the postmodern period of decomposition, a waxy substance called adipocere may form.

Stages of Decomposition:

1. Fresh (Hours after death): corpse looks normal on the outside and is still warm. Autolysis starts and temp drops. Insects lay eggs.

2. Bloated (several days after death): corpse emits odors of decaying flesh and appears swollen. Skin becomes marbled in coloration and insect activity decreases.

3. Active Decay (1-3 weeks): Body emits gases of decay with very strong odors and shows sign of darkened tissues and ruptured skin. Most body mass is lost to insects’ activity

4. Advanced Decay (3-8 weeks): corpse starts to dry out; most flesh is gone and adipocere is forming. fewer insects remain.

5. Dry/Skeletal Decay (2+ months): mostly bones remain

explain how food progression helps with the determination of TOD

The progress of food in the digestive tract continues as long as one is alive. If there is partially digested food in the stomach, death occured 0-4 hours after the last meal. An empty stomach with a small intestine that is full means that death occured 4-12 hours ago. An empty small intestine indicates that death occured 12 hours ago, and the person has been dead for more than 30 hours if even the large intestine is empty.

Scenario:
A body is discovered in a forest. The victim is found lying face down on a slope. The lividity on the chest and abdomen is fixed and purple. When the body is rolled over, the back shows no lividity. Rigor mortis is fully present throughout the body. The stomach is empty, but the small intestine is full. Blowfly larvae are present, mostly in a large wound on the victim's neck, and the most mature are in their 3rd instar stage.

Extracting Info and Linking to TOD:

1. Livor Mortis: The fixed lividity on the front of the body indicates death occurred more than 8 hours ago. The fact that the back has no lividity confirms the body was not moved after lividity fixed and has been in this face-down position since death.

2. Rigor Mortis: Full rigidity suggests death occurred at least 8-12 hours ago and likely less than 36 hours ago (as it hasn't begun to disappear).

3. Digestive Tract: An empty stomach with a full small intestine suggests the last meal was 4 to 12 hours before death.

4. Entomology: The presence of 3rd instar blowfly larvae indicates that insects have been colonizing the body for several days.