As soon as I realized this was happening I would take a crouch stance, and draw on him real slowly so as not to make any noise. Then I would give a loud "DROP YOUR WEAPON" as soon as Fred made eye contact with me. As the perp spins to engage me I would let a double tap go center mass. If the perp listens an drops his weapon I would kick it out of the way and have him get face first on the floor all spread out and hold him at gunpoint till the authorities arrived.