St. Ptersburg Revisited

I'm on the St. Petersburg Revisited level. I get the sniper's rifle and the ammo. But when I go into the building across from the one where the target is and get him in my sights and fire nothing happens. I have him dead in my sights and unload all the ammo and nothing happens he doesn't move, no windows break from the gunshots, nothing. I have even entered the building with the target, snuck up behind him, and tried to use the wire to strangle him but that doesn't work either. Is there something I'm missing here or some kind of trick to completing this level? Any help would be appreciated.