Gas him first instead of instigating him to shoot at shit?

Where is he in the house to gas him? Does he have any hostages with him he is threatening? Would those same hostages be harmed by the gas (medically frail or children)? Is he even still alive or did he shoot himself at some point and is already dead?

Those are just a few problems I can think of quickly with starting with gassing him without knowing everything they did because robots were in there.