I’ve read reports indicating that neighbors believe he tried to lure someone in to set it off. The front door was left unlocked, and techno music was left playing very loudly set on repeat, until 1:00 AM, when it shut off.
The neighbor lady in the apartment below him went up to ask him to turn down the music. She was interviewed and said the door was cracked but for some reason she didn’t push it open. That was her lucky day.