The assailant, if the story is true the way the vigilante said it happened, must have had a death wish.  Nobody in their right mind will shoot a police officer, knock him down and sit and pound on him while a vigilante stops and asks the fighting officer is he needs help, then runs back to his car and gets a gun and demands that the assailant get off the office or the vigilante guy will shoot.  Just did not happen that way.  The vigilante shot first and did not bother to ask questions.  Glad the officer did not die at the hands of the assailant.