Also consider he’d been drinking prior to the break in. I agree with you completely. Guy was there to kill nancy not Paul. Calmed him down saying he’s waiting for Nancy and won’t hurt him. Paul handled it well actually. Then the guy went for broke when he realized the gig was up. The murderer was only trying to stop a worse person than him and decided murder would be best. That was his mistake. We can’t solve this by murdering them. We have to use the law no matter how slow or unfair that is against the evil but these are the results.