This was one incident where the shooter was WRONG! He should never have confronted the man since there was no crime IN PROGRESS - he had his identity, and address know - allow the police to do their jobs.
I am wondering a bit now if this person had experience with the police and knew that they would not respond or that they had let this rapist go in the past? There are a few details missing here also to cause the shooter to act this way. (( IF he had a reason, that is ))
If not, he should be charged with murder.
He drew down on the guy without witnessing an assault in progress.