I'd just like to add to the above solution by saying that there are 23 stones that need to be scanned
The 24th and final message is unlocked when you scan the room mentioned above by Wottstar83
This room is located in the center of the security control room in the penitentiary. It is the guard tower looking room in the center of this control room.
To scan simply walk to the entrance of the room, and click and hold left bumper to scan.