Which, incidentally, is by popular demand of the players way back in the beginning, who were finding that a "only the last hit is responsible for the death" rule meant that they weren't getting many bounties in a RES because the police were kill-stealing them all. (No HazRES back then, of course)You hit somebody with stray fire and then other ships finished them off.
You contributed to their destruction and, as a result, you share responsibility for the murder.
When 99.9% of the time the rule works in the players' favour, it shouldn't be complained about the few times it doesn't.