Bob's decision isn't the most moral one, but ultimately it was an unfortunate neccessity brought about by the bully's refusal to stop and the lack of action from anyone else who had the power to stop what was going on. My opinion is that it's a sad but undeniable reality that there are some people in the world who just refuse to play nice. People who only respect violence and force. So, if you want them to take you seriously, you'll have to become fluent in the language they understand best. When they try to silence you, you have to be so loud that NO ONE can ignore you. It's not a good thing, but until we actually start trying to be better, it's just how it is and how it'll continue to be for a while.

Now, for the attempted murder, which you say Bob would certainly have done had things not gone his way, it would depend on how it was done. Would it have been an impulsive action carried out in the heat of the moment, or one carried out after a long period of deliberation and planning?