[Sawyer]

If we really wanted to make it complicated it might be able to be rigged so that there's a chance the assassin gets identified fleeing the scene or something, but that it's not automatic.
It could even be unit-dependent. I have a suspicion that an assassin with glamor would be almost completely undetectable, while something like a demonbred slayer would be pretty noticeable. Or one could always take the easy way and make it dependent on the assassin's pre-existing stealth value.