I can't feel any sympathy for him. I do feel he killed Allison, but I believe he knew what he was doing, and may well have planned it somewhat. He certainly knew what he'd done after the fact (IMO), yet he can't/won't own up to it.
I do think it's likely that Big Daddy was involved, at least after the fact. I think Mama would know at least some of it also. So no, can't feel sorry for any of them. I think they've all acted in such a despicable way, they make me feel repulsed.
It's weird, because I think I can sort of feel sorry for some criminals, even if the crimes are horrendous, but with this one, the deception and cover up, the refusal to help, or talk, takes all of that away for me.
I do think it's quite possible he has a sociopathic personality, in which case he was either born that way, or made that way, but they still know what they do, they just don't care. I can't feel sorry for him at all.
MOO