As the parent of a little girl about the same age as the one in this episode, I cried all the way through, especially when her father saw her on TV. I can understand why he had such a violent reaction, knowing he might have helped her if he hadn't got himself stuck in jail.
I can - almost - understand why the little girl's stepfather tried to cover up how she died, but he took it too far and now he's going to be in a lot more trouble. I can see why he falsely confessed, too - he must have felt guilty for falling asleep and not keeping a close eye on the kids. Yes, the other two kids were older, but it shouldn't be their responsibility to look after a small child.
As for the guy at the end, I think it's a grey area - after all, Catherine really was "just doing her job", but it's led to a lot of trouble for him. I can see why he reacted the way he did - he was only on the register for one silly mistake he made years ago, but at the same time he wasn't exactly honest, and hampered the investigation by lying about where he put the box. He just got trapped in a web of his own lies.
Oh, and that 'comedian' at the beginning was sick!