Al Pacino, "Cruising" (spoilers)

Can someone explain the ending of this movie to me? I just caught it on Cable and I “just didn’t get it”.

Was the ending insinuating that Al Pacino was the killer all along? Or that he just killed his neighbour because he felt like it?

Paul Sorvino’s character says something like “6th Precinct? Oh my god!”. At the very end. It was earlier revealed that officers from the 6th precinct were allegedely forcing gay prositutes to give blowjobs in their squad car. Was Pacino’s character from the 6th precinct? Having Al as the killer makes no sense, at least how the movie presented itself.

Also, can anyone tell me what the heck was with the huge black man in the jock-strap slapping people during the interrogation? That entire scene just seemed surreal.

William Friedkin, the director, is on record as saying that he doesn’t really know what the ending means either. He’s also on record as saying that all of the murders were committed by one man and that the killer is sterile, which doesn’t explain why sperm was found in one of the victims.

As for the big black man in the jockstrap, don’t try to understand him. Just enjoy him.