This can be achieved during the Paris Cathedral level. Locate a Metro station (a station you eventually have to proceed to after completing the main objective at the Cathedral). Proceed through the station until you find a mechanic and a repair bot inside a closed off room. Directly opposite them is a locked up cafe. Pick the lock on the door and read the journal on the table next to the window. Then get into the mechanic room using a grate behind it. Talk to the mechanic and choose the dialogue option that threatens to expose him. Then leave this room and talk to one of the police officers nearby. Return to the mechanic and continue this dialogue and you should get the achievement.