Tormented Souls

Once you solve the W-2F West Wing Corridor combination key puzzle and gain access to the Intensive Care Corridor, you will meet the Priest for the fourth time in Room 2B. In the adjoining room, you will be able to access the alternate version of this corridor, where you will find an armless mannequin, as well as the Parchment Scroll, the Hammer and the Mannequin Arm in the adjoining rooms.
 

After obtaining these items, return to the reality through the mirror and solve W-2F Room 2D- Judge's Podium Puzzle (check the Additional Resources Suplementary Guide section for more information on how to solve this puzzle) and you will obtain the Staple Gun, with which, after adjusting it once, you will be able to "re"-attach the arm to the mannequin. Return to the reality one more time and proceed to talk with the Priest to get the trophy.