I think he was a maintenance man in the building....
No - that was a completely different violent crime event, committed several days before, in a different building, by the same man.
I think the dead CEO female might have been purchasing drugs and/or engaging in anonymous sex.
The dead CEO lived in the building. Her company was located in the building.
Why would she be sitting alone in the lobby, at 9 PM on a Friday night, and then let a complete stranger in the door, and voluntarily get into the elevator with him?