To unlock this mission, you must first gather evidence in some of the other campaign missions.
Wristwatch: In the server room during Desperate Measures.
Cassette Tape: After entering the SATCOM building in Echoes of a Cold War and just after finding the body with the crossbow bolt, you will find the tape on a desk.
Ledger: In Brick in the Wall, turn right at the top of the stairs in Franz Kraus' apartment, and enter the room directly ahead of you. The ledger is in the drawer to the right of the bed.
Once you have this evidence, you must first solve who the three aliases are in a list of suspects. These will be randomised for each playthrough. You are looking to work out which person is "Bearded Lady", "Strong Man" and "Juggler". Use the Wristwatch to determine the gender of each alias, then crossreference the dates and locations in the other two pieces of evidence with the movements of the individual suspects.
With the suspects selected, the mission can be started. Completing the mission after correctly guessing the suspects will unlock the trophy.