http://www.philly.com/philly/blogs/harrisburg_politics/Two-l...
> Confronted by a gunman just blocks from the state Capitol on Tuesday night, a Democratic legislator from Northeastern Pennsylvania pulled his own weapon and traded fire with a would-be robber.
Remaining question is to look up the legislator own voting record on the issue of gun control.
http://www.ijreview.com/2014/03/125342-armed-man-gathers-peo...
https://www.youtube.com/watch?v=yqkqzsIjujI
http://bearingarms.com/concealed-carry-permit-holder-stops-s...
I don't think that would fit into the case of "preventing a crime", the guy shot 3 people then started leaving, before he got shot
However, continuing to extrapolate from this report, neither police (http://en.wikipedia.org/wiki/Tennessee_v._Garner) nor civilians are allowed to use lethal force on someone who's ceased threatening and is simply fleeing. If a case cannot be made that the threat was still there, guy who shot him should have been charged.
Your post may seriously be the stupidest thing I've ever read in my life.