There is no evidence of that. He was already being tailed by the cops for raping a woman and setting her on fire, along with her boyfriend.
He was just a criminal who gained access to a building and killed the victim. Lots of people are too friendly and the access of security gets compromised for that character trait.
I think he might have been a maintenance man because the other incident where he attacked a couple in their bedroom he gained entry by banging on the door and requesting for them to come out because there is a flood. So either he pretends to be a maintenance man or he actually was one.