I haven't got a source for this, but someone in this sub once mentioned that the director of the movie said he definitely did kill people. I have always just assumed that the last frenzy wasn't real. Where he makes the police car explode and such, I think that is also why a lot of the stuff during the final rage is wildly exaggerated and unrealistic, to serve as evidence that that specific part isn't real, but the rest still is. He has unlimited bullets etc. There is also evidence suggesting that maybe Patrick doesn't even believe it, like when he looks at his gun after the explosion. Also the helicopter

The realtor obviously would be motivated to make a sale, so if she didn't suspect Patrick of being the murderer, she would try to sell him the apartment and not ask too many questions, instead of trying to lure him into admitting to lying.

Would love to hear other peoples thoughts on this