That makes the proposition largely unfalsifiable. That is---and this is a very minimal report---we can't know if someone who momentarily stopped shooting would continue.
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.
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