There are ways forensic anthropologists and osteologists can determine cause of death by studying other details of the skeleton. Even old ancient ones.

ie. If there’s an injury on the skull and also damaged bones in the arms and hands, one can determine that the person was assaulted and died. If there’s an injury on the skull and fractured spine but no signs of struggle it’s possible the person died falling off a horse. These are overly simplified examples — the experts can take a million things into account just by studying the bones and come to solid conclusions with evidence to back it up.