Forensics

• All mammals preoduce their own body heat (at 37 in humans)
• these reactions slow after death
• cooling follows a curve (assuming it is 35 at time of death)
• only relavant for 24 hours in temperate or cool conditions
• Cool at a rate of 1.5-2 C per hour for the first 12 hours then 1C per hour after 12 hours

Factors

• Air temperature
• Clothing
• Body Weight
• Body Position
• Humidity 

• Autolysis is the first stage, where enzymes (from the intestine) break down cells
• Putrefaction is bacteria escaping the body from the intestines that begin to "melt" the body

Signs

• Green discolouration in skin that turns to blue/black
• Gas or liquid blisters appear on the skin
• Gases build up in the body cavaties
• Body begins to smell
• Tissue decomposes, body deflates and the gases are released
• Tissue shrinks and decay slows 

The study of insects (in particular after corpse death)

• Take samples from the corpse  measuring maggot mass, various temperatures
• some are killed to determine age
• some alive fed to determine species
• Provides a minimum time of death
• Stages of growth are always consistant in length 

if normal development time for an egg is subtracted from the date of pupation then you can roughly work out when the eggs were laid. This can give an estimate of the time of death. (only an estimate as it is impossible to tell how long it took the flies to find the body)

After death the muscles will stiffen

• The muscles cells will be starved of oxygen and aerobic reactions will stop
• Respiration becomes anaerobic and produce lactic acid
• pH will fall, inhibiting enzymes and halting anaerobic respiration
• ATP is no longer produced so the bonds between the muscle proteins will become fixed
• So muscles can no longer shorten or lengthen freezing the joints into position

Temperature of body Stiffness Approximate time since death
Warm Not Stiff Less than 3 hours
Warm Stiff Dead 3-8 hours 
Cold Stiff Dead 8-36 hours
Cold Not Stiff more than 36-48 hours

Factors affecting rigor mortis:
Temperature, Physical excertion before death, Fat levels in the body, Age, Illness

This will only give you a frame of time that the death could have occured. Other methods should be used to give more precise times of death.