The CCTV footage would seem to make those first two somewhat less likely:

"One of the law enforcement officials said a surveillance camera had captured video of Mr. Saleh in the building’s elevator with another person who was wearing a black suit and black mask."

"On the video, the elevator door opens and Mr. Saleh goes into the apartment, the official said. The masked person follows directly behind him, and the two immediately start to struggle, the official said."