I'd say the person who beat the crap out of the cop should be tried and jailed for that just like the cop who beat the crap out of the guy with his hands up should be tried and jailed.
Also, if a mass killer drops his weapons and starts running, I'd agree that it's ok for the cops to shoot him if they can't otherwise catch him. Otherwise he might do it again. So I guess we've found a second case where it's alright.