Your thoughts on this heinous Japanese crime 1888-89. (Read details first).

For those of you who are familiar with the kidnapping of Junko Furuta, and the torture she went through for 44 days.
I came across this story a couple of years back, and it traumatized me. About a minute ago I came across it again after so many years. One of the four boys who tortured her was a teenager, I’m sure the other three weren’t that old either.
What I’m not able to comprehend is what would make these young boys do something so evil. I’ll sound naive if I say ‘What would make anybody do something so evil’.
Yes, the world is a bad bad place, but what they did to her, makes me bawl like a baby. I don’t get it.
For those of you not exactly familiar with the tortures she went through please have a read first.
I just want your thoughts on the matter. Don’t twist my question around. Just your thoughts please.