Killing Player?

Is there a way to get the player who killed a unit, when the killing unit = no unit?

Example: Player 1 casts doom on a ghoul, the ghoul dies.

How can I get, from a trigger, the player who killed that ghoul?

Owner of (Killing Unit) doesn't work, since Killing unit will return no unit.

Any ideas?

How would a player cast doom on a unit without having a unit that can cast doom?

unless you remove the unit before the trigger activates, the killing unit will always be the unit that casted doom. Even if units die, they still exist unless removed.

Oh really? I thought that it would return no unit if the unit that cast doom wasn't on the playable map (dead for example).

Thanks.