How do you know he didn't have a gun? You were told her has a gun, you get to the house and the person letters his arm and then raises it and starts pointing it

How do you know he didn't have a gun? You were told her has a gun, you get to the house and the person letters his arm and then raises it and starts pointing it at a fellow officer... What do you do? I don't think this particular incident is as cut and dry as you think it is.