You mention: They stop the decomposition by refrigeration. This is important because they want to accurately estimate the time of death. This can make a huge difference in who might be guilty in a murder case.
In a case like this, the time of death has to be determined before the body is refrigerated. Refrigeration is a way some perps use to make it difficult to determine the time of death. Some think the reason windows were open at two Rhoden homes was to change the ambient temperature and mislead the times of death. The time of death is determined by body temperature and ambient temperature in bodies found soon after death.
How Is Time of Death Determined for a Crime-Scene Victim?
According to Lawrence Kobilinsky, a forensic scientist and professor at John Jay College of Criminal Justice, time of death on a fresh corpse can best be ascertained via a measurement of core temperature. “It’s not linear,” Kobilinsky cautions. Still, he says, “most examiners use a formula to…come up with an approximate range.”
For the first several hours after one’s heart has stopped beating, the body’s core temperature drops towards ambient temperature (i.e. room temperature, if indoors). The formula approximates that the body loses 1.5 degrees Fahrenheit per hour, so the rectal temperature is subtracted from the normal body temperature of 98 degrees. The difference between the two is divided by 1.5, and that final number is used to approximate the time since death.
Of course that simple formula only works if several factors are assumed constant: that the ambient temperature hasn’t changed since the death… or that the victim was discovered clothed and in the air rather than in, say, a bathtub full of water. But according to Nathan Lents, a forensic biologist colleague of Kobilinsky at John Jay, things are rarely so simple.
“A body in the field—rarely are you so lucky that it’s 72 degrees all day and all night long,” he says.
In a climate-controlled environment, it will take six or seven hours for a body to reach ambient temperature. Further biological evidence taken in conjunction with core temperature helps better fill out the picture.
Blood starts to pool
One of those factors is livor mortis. Once the heart stops beating, blood stops circulating and responds instead to gravity, pooling into the parts of the body closest to the ground. This causes marbleized discoloration of the body. Livor mortis generally begins 20 to 30 minutes after the heart stops beating, but passes through stages. Between 30 minutes after death and approximately one hour, for example, the skin will “blanch” when pushed, with blood leaving the area where pressure is applied. After that, once livor mortis has fully set in, blanching ends.
In addition to helping with time of death, livor mortis can also show investigators that the body has been moved if the markings of livor mortis don’t correspond with the position the body is in.
Becoming a stiff
About three to six hours after death, rigor mortis begins to affect the corpse. Muscles lock into place, beginning with small muscles in the head, the eyelids and the jaw, before moving on to fingertips, neck and then larger muscles. Rigor mortis sets for 18 to 36 hours before dissipating.
Once livor mortis, rigor mortis and ambient temperature are all in place, determining a precise window of death becomes trickier.
