My thoughts on the ending.....
I personally think that many on here are overthinking when it comes to the ending. But then again, the ending is left ambigious so therefore there is no right or wrong answer. Anyways, on to my thoughts:
I think that Al Pacino was NOT the killer, nor did he kill his "neighbour" at the end of the film. his neighbour was killed by his boyfriend, there is a seen sort of forshadowing this when Al Pacino is sitting in his room listening to them argue. The boyfriend seems violent and very angry with him. Pacino, being a cop, senses that his boyfriend is very violent and capable of doing something terrible. That is why in the next scene when they are having a cup of coffee together, Pacino says: "I wish there is something i could do for you". He feels sorry for him that he has to take such abuse and is worried that his boyfriend may do something worse. He then later tries to break into the house in an attempt to f ^ ck the boyfriend up because he knows just what he's capable of. His boyfriend then pulls out a knife and threatens to kill Pacino. Pacino leaves and that is the last you see of the boyfriend. (sorry i don't know their names).
Well, Pacino's fears came true. Eventually, the guy's boyfriend DID end up killing him with the very knife he used to threaten to kill Pacino.
Pacino staring into the camera again is just to show a bit of character ark. In the beginning of the film he seems like a very young, naive man who takes things very light heartedly. He laughs when the detective askis if he hever got a BJ from a man instead of getting personally offended, he is always smiling and laughing, and it seems that he takes the job without really thinking about it. This is because he is still very naive and does not look at the consequences the job may bring. He just kinda looks at the photographs on the wall and says: "okay sure!" and that's it.The assignment later begins to take a toll on him. You can see this throughout the film as Pacino's character gets grumpier and has more of a temper. His naiveness and lightheartedness begins to go away and by the end of the film he is almost a completely different person. It's as if he has matured out. By the end, he is left exhausted and knows how messed up and ugly the world can be. He learns something dark and grim from the assignment he has taken and it is something that will never leave him. That is the reason why he stares so grimly in the camera. His character is not as innocent and naive as before. He has seen society's dark underbelly and cannot walk away from it.
Now here's where i get confused. There are theories on here that there never really was ONE killer, but rather a bunch of random ones and it was just the cops wanting to cover it up. Well, that maybe true, but if it WAS just one killer, then how come ALL OF THEM said the exact same sayings. The "who's here, you're here, i'm here" and the "you made me do that" couldn't have been said by someone completely different. That would have been like the biggest coincidence ever. Since the killer ALWAYS had the same voice and said the exact same things, i'm gonna have to say that he was probably the same guy. Anyone have any thoughts??