California Code, Penal Code - PEN § 194

To make the killing either murder or manslaughter, it is not requisite that the party die within three years and a day after the stroke received or the cause of death administered.If death occurs beyond the time of three years and a day, there shall be a rebuttable presumption that the killing was not criminal. The prosecution shall bear the burden of overcoming this presumption. In the computation of time, the whole of the day on which the act was done shall be reckoned the first.