From what I have read the suspect had a love hate relationship on his being a john at these establishments and took out his dogmatic fantasies on various massage parlor attendants.
This is what happens when establishments like this are in this gray zone, they need to be legalized so that proper security can meet crazed individuals like this at the door and disarm him or provide a lethal defense to crazed maniacs.
A team of bouncers that are ex football players or MMA fighters or boxers could have disarmed this man or took him out with lethal force if this was a legal establishment with metal detectors and bullet proof doors and windows.
PS here's a news report one slain victim was a White woman, but the other 7 victims were Asiatics, note no customers were killed, so there was deliberate intent which would stop any insanity defense...