CSF should be collected within
Cistern fluid is examined. The amount of potassium increases at a constant rate in relation to the temperature of the body during the first 20 hours. The concentrations of sodium,calcium and magnesium have no obvious relationship to time since death. Ref: K.S.Narayan Reddy's Synopsis of Forensic Medicine and Toxicology, 29th edition, Chapter 7, page-98.
4-6 hours after death
12-16 hours after death
16-20 hours after death
20-24 hours after death
Death and postmortem changes