Unfortunately I don't think you can. The trigger would need to be "A player busts out", but there's no variable that would allow you to determine that the hitman won a specific prize. In fact most of the variables apply to the player busting out, not the hitman. I'll have to look into that to see if/how that can be done.
Apologies for reactivating this thread, but...
I think the OP was looking for the trigger that fires when a previously identified player is busted out, and not looking to identify the hitman.
.OP manually places a bounty in Player X at start of.tny
.when player x busts out, fire an announcement that says something like "Bounty Alert! Someone just took out our last winner and earned their Bounty" (or.similar)