Get Even

This achievement can be obtained during the second visit to Building B. You'll get to a part where an inmate is behind some security controls and, depending previous decisions made in the game, he will leave this place or we'll have to kill him. After this, we can enter and there'll be a security camera feed on a screen and three switches, you'll need to activate the left and right ones, then the screen will show other inmates getting out of their cells. You can proceed to activate the switch in the middle and the achievement should trigger after moving to another room.