Cruel would be if we forced them to endure simulators that let them know what it feels like to burn up in a building, jump from a multi-story burning building, be crushed by a multi-story burning building, or be blown apart by a [insert explosive of choice here].
Appropriate. But, cruel. ;)
It's difficult, but I can forgive their actions. That doesn't mean I forget what those actions were. Or that I lose sight of that, if left unchecked, there are subsequent actions they'd be capable of doing. I leave the appropriate punishment here on earth to the authorities. I leave the final judgment stuff to God. However, only those who don't understand the bible would think that the second tower is an example of turning the other cheek and that we should just let bygones be bygones and set 'em free!