I'd like to comment on this thread. Having been a cop for many years, I have my own take I'd like to share. If everything I'm reading is correct. This Officer should be arrested.
First off... If he noticed what he percieved to be a dangerous situation the most prudent thing would have been to "call the cops" and allow uniformed on duty officer to investigate the situation. There was no emergent situation requireing imediate action, there was no ones life in imminent danger, There was no evidence of a crime being commited. Only the articuable suspicion of the possiblity of a crime being commited. I dont believe this off duty officer had any right to enter the home of a citizen without a warrant, or a reasonable belief that he could under exception of a warrant.
According to the information available... This was a bad shooting.