After watching this video, I have to say that the cop showed tremendous maturity, restraint and even compassion. I don't know if you notice but when the guy starts walking forward, the cop is clearly walking backwards, retreating while giving the guy repeated orders to "put the knife down".
I actually feel bad for the cop. Its one thing to have to shoot a clearly "bad" guy who is hurting people. Its an entirely different thing to have to shoot someone who may not actually be a bad guy, but is clearly using you to commit "suicide". Its gotta screw with your head.
+1