Did you read the article that you linked to? What the article said was that he didn't know that the gun was loaded - not that it fired itself.
From the article:
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Wafer told police he didn't know his gun was loaded and said he shot the unarmed teen by accident, according to a recording played to jurors last week.
"What happened here?" Sgt. Rory McManmon asked, according to the recording.
"A consistent knocking on the door, and I'm trying to look through the windows, but every time I look through the windows and the door it's banging somewhere else," Wafer said on the recording. "So I open up the door, kind of like who is this? And the gun discharged."
"I didn't know there was a round in there," he tells McManmon on the recording. "I don't get it. Who's knocking on your door at 4:30 in the morning? Bang, bang, bang -- somebody wanting in."
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For you to try to state anything else is just nonsensical. I don't believe that you actually believe that the gun suddenly decided to fire on its own - you have to be trolling.