Don't confuse this issue with the fact that they didn't announce and were at the wrong house. These both allowed the unfortunate circumstance to come about but were not deciding factors bringing about the actions that followed. Proper announcement would have likely stopped this from happening but the fact that they didn't didn't MAKE it happen. If he did in fact open the door muzzle first, he was in the wrong. It is illegal to confront anyone that way when they have shown no aggression or given you cause to fear for your life or safety. If this was the case the officers responded properly to illegal use of force. Take to cops out of the situation. If a civilian knocks on someones door and is greeted with the muzzle of a gun they (could/would/might) be justified in shooting the homeowner. The homeowner used illegal force. Again just because an action could have made the situation better doesn't mean that action was the reason it went bad. I believe the cops could be acquitted of any wrong doing if the were met with an aggressive homeowner with a gun pointed at them.