Shooter's identity questioned in the East End, reportedly (3)
I believe the answer is:
uzi
'shooter's' is the definition.
(type of machine gun)
I can't explain the remainder of the clue.
(Other definitions for uzi that I've seen before include "Type of submachine gun" , "Israeli-designed sub-machine gun" , "Israeli sub-machine gun" , "kind of weapon" , "killer" .)