Anyone ever seen someone when they "blackout"? I made my boyfiend quit drinking because of that. I could always tell when he was in blackout mode because his eyes kind of glazed over and all of the sudden no matter what anyone said, he would get defensive or just plain mean with his tounge. (The guy doesn't have a mean bone in his body until he blacks out) It finally took me tape recording him when he was like that to scare him enough to quit. I guess he didn't believe me before. Kind of like "I don't remember, therefore it didn't happen."
I think there is a possibility that this guy was so blacked out he didn't know what he was doing. However I agree it is highly unlikely, as what was he doing at the house in the first place. And why the hell did he start the fire? If I woke up like that, even if I knew I did it, I would go straight to the police.
I also saw a law and order episode a couple weeks back, with this same storyline. Creepy. The guy didn't do it and had been in prison for 10 years.