The man was in hot pursuit, the police were not there yet, he had an opportunity to apprehend the culprit and recover his goods, he had no way of knowing that this particular one of the robbers who had just forcibly held him and his wife captive had or did not have a gun . . . the bad guy turned toward him—bang, bang, end of story. Give the man a medal and go after the other robbers.
When seconds count the police are minutes away!
As long as the perp is truly dead, kinda hard to dispute.