I'll have to read this thoroughly over the weekend, when I can put some thought into it.
At first glance though, it sounds like a jealous husband shooting his wife's lover. The issue could be that adultery is a felony in GA. He shot to prevent a felony from being committed on (by) his wife. Kinda twisted logic, but could possibly be a decent defense.
Like I said, I'll have to read it in its entirety over the weekend. All I did so far was glance over it.