Prison Break: The Conspiracy

The first real sneaking mission. Start in the janitors closet through the grate on the wall. As soon as you exit the grate, walk toward a closet and hide in it till the cop has got his coffee. Walk to the room on the left then jump up to the roof grate with the shelves. You then have a quick-time event. Press 'Y' repeatedly till 'B' pops up. Press that once, and the achievment should unlock.