How do I find out Who fired something?

The part that is giving me trouble is that I'm trying to figure out who fired the crossbow, so you have the following vars

function CrossbowImage::onFire(%this, %obj, %slot)

%obj does give me an index and I saw somewheres else that this is the key to the holders object, but when I call gettaggedstring it crashes. So I assume I'm doing something wrong..... so how do I find out who caused the onfire event?

Vince