you were a victim of this illegal lab. You had a really strong quirk, when you were trying to escape the lab with your friend, the boss, shot him and you got pissed and killed everybody there. It's been months since that happened, you were certainly in a cell, locked up. Deku and the others were trying to figure out why anyone, let alone a kid, would kill everyone in the lab, they didn't know what was happening in that lab. Deku:"look kid, if you just told us what happened,we could help you"