capx please.
How are the zombies moving? Do they have a bullet behavior and set their angle to the civilians every tick? If yes, say hello to Turret behavior. It automatically sets your sprite's angle to another sprite, or a group of sprites. You need to add the objects to the behavior on start of layout (forgot the condition's name), and it rotates to look exactly at it's target. And if you search Turret's properties a bit...