This is my escape from a 3-1. I expected it from the beginning. If you don't know, if you have a "tactical advantage" you can try to get away from or fight the 3-1. If you try to fight or evade a 3-1 and end up dying, you can get in trouble.
Ask the guy if he'd like to wave his rights and if he does, take him to a panic room and process him there. Another option would be take him to a panic room and wait for 5 min or so, if the guy shooting isn't hitting anybody and isn't pushing, you can deem him "not a factor", in which you can continue processing.