Is there any sort of function to find the damaging player?

There's 2 functions in the script I'm creating for my game.

One is LockOn() , it makes your player lock on to any person in the game.

Well say I wanted to only run LockOn() to the SPECIFC player that DAMAGES me

How would one do this? I already know how to run functions and stuff, but I have NO idea how to define one as the player that did the damage. Yes, there's "getnearesttorso" and stuff, but that doesnt help much when there's a lot of people around me in the game.

I've asked people, read so much of the wiki and google, and can't find one answer.. Any help would be greatly appreciated