When a burglar breaks into your residence while you are home are you going to break out the tea and crumpets instead of the Glock???
No, but when the girl is lying on the ground with multiple gunshot wounds, walking up to her and emptying the clip into her head, and then hanging out with 2 dead bodies at the house for a few days is not the correct course of action either.
Hell no. In states with a Castle Doctrine, if someone breaks into your house you are automatically granted the benefit of the doubt that you were in fear of your safety and deadly force was justified.
However, when someone is laying on the ground, gasping for breath, the threat has ended, and your justified use of deadly force has ended. Did you read the criminal complaint in post 10?
Smith states several minutes later he again heard footsteps on the main floor of his house. Smith stated that another person came down the stairs into the basement where he was sitting. Smith said he waited until he could see her hips and then he shot her. After shooting the person she tumbled down the steps. Smith stated that he tried to shoot her again with the Mini 14 but the gun jammed. Smith stated that, after the gun jammed, the woman laughed at him. Smith stated that it was not a very long laugh because she was already hurting. Smith acknowledged that this made him upset. Smith told Investigator Luberts, "If you're trying to shoot somebody and they laugh at you, you go again." Smith then pulled out his .22 caliber 9-shot revolver that he was wearing, and he shot the female several times in the chest. Smith acknowledged that he fired "more shots than I needed to." Smith stated that he then dragged the female's body into his office workshop and placed her body next to the man's. Smith stated that the female was still gasping for air. Smith stated at this point he placed the handgun under the woman's chin and shot her "under the chin up into the cranium." Smith described it as "a good clean finishing shot." Smith stated he wanted to end her suffering. Smith acknowledged that neither the male or female had a weapon, but maintained that he was fearful the entire time that they might have a weapon."
It was a clean, justifiable shoot right up to the point where he stands over the woman and shoots her several times while she lays motionless, when he dragged the bodies, and administered a coups de gras to the female as she takes her last breaths. You are demonstrably no longer in fear for your safety, and that, plainly, is second degree murder.