For once, because I detest the basic concept of the death penalty. Nobody's helped with the death of someone who poses no immediate threat to anyone, and provident judical actions are seldomly worth the error ratio. But that's a big one, so let's get particular.
Secondly, it's easy to call it sinister child murder, but we all know things weren't quite as straightforward. I'm not saying he isn't downright responsible for the death of a civilian family, but his intentions and the way it was carried out was importantly different:
He was a coward, and a greedy one at that, but not a psychopath. When it comes to his case, that means everything to me - a murderer cannot be redeemed, but he didn't have them killed because he enjoyed it or thought it was necessary, he didn't stop the slaughter because he was scared to be blamed - knowing it's a terrible thing.
Thirdly, he's a different man now. As far as I'm concerned, Thom is the most "good" of all the companions, because altruism means everything to him. It's disgusting how he got there, but he is literally doing everything he can do to make it up. He has no personal agenda, other than doing good until he croaks - not a lot of clean living people can say that of themselves.
Fourthly, he's my bro.