I saw a news piece on Fox (?) in which a survivor described how someone had physically blocked the rear exit of the building to keep people from escaping. That makes it at least two perps involved in this shooting.
It was actually a patron at the establishment who escaped with another patron, and then they both blocked the door when they heard the shooting getting closer. He came forward about it, and was despondent because of the others who'd tried to escape but couldn't after he blocked the door.
I too originally saw this, but then I saw an interview by one of the victims. I think he admitted to blocking an exit door so the gunman couldn’t escape. Not sure if it is one and the same. Also, 20/20? I believe interviewed a victim who said the terrorist said he was the fourth shooter. Now, I don’t know if this was to lie to law enforcement fooling them into thinking it was more than just him, or if there were more accomplices.