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.