The problems of measuring time of death from rigor mortis
Source: Homicide: A Year On The Killing Streets: David Simon.
“Without a time-of-death estimate based on body temperature, a medical examiner is aided only by the degree of rigor mortis (the stiffening of the muscles) and lividity (the settling and solidification of blood in the dependent parts of the body). But the rate at which any postmortem phenomenon occurs can vary widely, depending on the size, weight and build of the victim, the external temperature of the body at the time of death and the temperature or conditions of the death scene.”
“Moreover, rigor mortis sets and then disappears, then sets again in the first hours of death; a pathologist would have to examine the body more than once – and hours apart – to assess the true status of rigor correctly. As a result, detectives seeking time-of-death estimates have become accustomed to working within a spread of six, twelve, or even eighteen hours.”
“The truth is that medical experts can often provide no more than a rough guess as to the victim’s time of death.”
In addition: To match the DNA coding of human hair at least one entire hair with its root intact is needed.