another method, using format:
unit addevenhandler ["killed",{_this exec "killer.sqs"}]; unit addeventhandler ["dammaged",{_this exec "dammaged.sqs"}]
init.sqs
TRG_counter = 0
killed.sqs
call format ["killer%1 = (_this select 1)",TRG_counter]
;insure that the other EH gets the right counter value
~.1
TRG_counter = TRG_counter + 1
exit
dammaged.sqs
call format ["?(killer%1 != player):exit",TRG_counter]
_area = _this select 1
?(_area != "hlava"):exit
titletext ["Head Shot","Plain",0.1]
exit
untested, but it should work