At that time, yes. But afterwards, it would not be considered so as they were fleeing the scene. At that point it is revenge, and while I'm good with that, here in Iowa it would get you multiple years in jail. I don't think it's worth it.
Groups here are working to change the laws, but not getting very far at this point.
A cop can use deadly force to prevent a violent felon from fleeing. Including a shot in the back, as cops routinely shoot at fleeing suspect vehicles.
A citizen should have the same right.
Someone who has already demonstrated an intent to kill should not be given the opportunity to get away.