Chapter 7 - Ghost Girl's Messages (4) | Collectibles Murdered: SS Guide

At the church, after you visit it for the next time, you will find the last message. After you start the "Search the Upper Floor For More information" main mission, climb up the floor, to the first floor. The stairs are at the end of the corridor, from which you walked out into the courtyard. Climb upstairs and enter the room the closest to the window. Approach the wall and reveal the message. You will obtain a message: Staircase.

You have already revealed all of the messages.