Trigger Question

In my map I have nuetral passave buildings called artillery. They have the ability select hero, so any1 near them can use attack ground to use long range attacks.
The problem is that i need to make a trigger that gives the player who used the attack ground a kill if the artillery hits and kills an enemy (i have a variable-integer array to keep track) Any one know how I could do this?

Im not sure if this is what you want; i dont know if the building is firing, or the hero. IF the hero is indeed firing, then you want this:

Events:
A unit is attacked
Condions:
(attacking unit) equal to (your hero)
Actions:
Unit - Kill (Attacked Unit)