How many years has an attorney prosecutor to investigate this cases? I mean both Canada and USA. In my country, if something like this is considered violating

How many years has an attorney prosecutor to investigate this cases? I mean both Canada and USA. In my country, if something like this is considered violating human rights, then the general prosecutor could re-open the case, it doesn't matter how many years after (this was intended for investigations on the disappearances during last dictatorship, but I think our constitution abides my reasoning if something like this happens).