I will assume that the evidence is correct, and that the man did pull a knife and slash the officer. I support his decision to defend himself. It would be nice if he had a reliable, non-lethal way to incapacitate the man, but if it's a guy with a knife versus a cop who just got slashed, I know whose side I'm taking when the guy gets shot.
Saying that the officer should've shot at his leg or arm, both moving, small (compared to the torso) targets, is not reasonable, because there is no guarantee that the officer would be able to disable the attacker and protect himself. A baton is not a good option, nor is pepper spray, because both require close proximity to a knife-wielding attacker who already slashed the officer.
As for the question about the man's disposition, his friends and family are naturally inclined to defend him, as they don't want th consider the possibility that someone so close to them would try to kill an officer. It's not difficult to hide the fact that you carry a knife, after almost two years of carrying a butterfly, my mother saw it (and confiscated it
) for the first time last week. The article didn't mention what type of knife was used, but I think it's safe to say that it would be easy to conceal.
I'm going to give the benefit of the doubt to the police on this one, and believe that the officer acted properly unless an investigation proves otherwise.