Another factor forensic investigators look at in a dead body is rigor mortis this latin tern describes the state of a dead body a few hours after a person dies the joints of a dead body stiffen and become locked in place rigor mortis is caused by chemical changes in the body after death due to oxygen depletion and the buildup of calcium when a peason is alive the calcium in a body is carried outside the body's cells this allows muscle fibers to move but since a dead body is no longer receiving oxygen calcium builds up causing the muscles to stiffen up and contract