Ben, if your saying therefore that I've got to accept that some individuals have deep-rooted issues that impact on their actions then of course this exists. But on the flip side, there's no evidence of this in this case is there- you in turn have to accept that some people are just nasty pieces of work.
Perhaps you could say the legal system failed him, it didn't set it right. I prefer to say that it failed the 3 year old girl who was subjected to kidnap, rape and torture and the hands of a man the law saw fit to walk the streets.
I'd say the legal system failed both of them, obviously it let the 3 year old girl down. But it also let him down, if he was still in a mental state to commit such crimes then there is know way he should have been let out.
I'd still say that the 'lock him up and throw away the key' mentality is not the way to go. If after a lot of counciling and psychotherapy, it seems he's more mentally stable and increadibly unlikely to re-offend, then of course he should be given the chance to restart his life, under supervision of course.