Looking for an old manga

So I read this like about 7-8 years ago so I don't really remember much about it but in the manga 7 boys were captured and detained in a school where they have to face trials and pass them to get out of there. Now the interesting part about the manga was that each of the boys were criminals and because of their crimes they had one body part of their cut off. The mc was a murderer so he had his memories removed and the reveal was the twist of the story.