Livor mortis

It is a settling of the blood in the lower, or dependent, portion of the body postmortem, causing a purplish red discoloration of the skin.

Livor mortis starts within 20–30 minutes, but is usually not observable by the human eye until two hours after death.

Fixation will begin to occur during this timeframe, causing the patches to be unaltered due to movement.

[4] Coroners can use the presence or absence of livor mortis as a means of determining an approximate time of death.

[3] Among coroners and other investigators, such as homicide and forensic detectives, livor mortis is not considered an exact way to measure time of death, but rather as a method of approximating it.