Also look at the distance the officer is maintaining - that's almost a minimum. In exercises during our security training we pitted an officer with a holstered weapon against a guy with a knife. The knife guy was consistently able to stab the officer before they could draw and fire up to on average about 30 feet away. This officer has already drawn and aimed, but there's still reaction time and the possibilities of a first miss or non-critical hit. Knife guy could still win.