heres some clues
Rigor mortis can affect a person quicker, if they involved with a struggle or fight?
Physical exertion just prior to death: If someone dies while engaged in strenuous activity like exercising or struggling against drowning, rigor mortis can set in immediately. This instant onset, sometimes called cadaveric spasm, happens because the person's muscles, at the moment of death, were depleted of oxygen energy and ATP. This is why the victim of a violent attack may still be clutching the attacker's hair or a piece of clothing.
warm temperatures can also set Rigor mortis faster too, as with illness or age