I agree the guy should be criminally prosecuted, but I'm not getting why 2nd Degree Murder is such a stretch. The guy opened his front door, the girl was standing on the other side of a screen door, he pointed a shotgun at her face and pretty much blew her head off through the screen door. He was in no danger; he knew he was in no danger. All he had to do was leave his door locked and call 911.
If this isn't reckless disregard for human life, I don't know what is.