In the second floor of the Police Station, the door for the room Linen Room is locked with a key Pink Diamond. In order to enter this room, you basically need that key, but you can only get this after you’ve completed collecting all of the Medallion and able to enter the Underground Facility.
How to Get the Pink Diamond Key
To get it, you need to go to the Police Station B1 at the Morgue room, from the Undeground Facility, just head to the right side door. Then find the door for the Morgue.
Inside the Morgue there are morgue fridge, open those fridge one by one or you can just simply open the last 2 fridge on the left. From there, you’ll be finding a dead body wearing black clothes. Go to his head to get the Pink Diamond Key.
That’s it! Hope this help you find the Diamond Key.