This walkthrough is for Case File 03: In the Shadows in Gotham Knights.
3.1 – THE KEY
Travel to the roof of the Gotham Gazette, which can be found in the southern part of the West End, and locate the door with the owl symbol on it. Head inside and work your way through the building. When you reach the large room, scan the letter on the letterbox. Next, look for the table to the left of the letterbox. Interact with it to start an investigation. Mark the Ofasiede Card and the Brass Peg that points west towards the Gotham River. Next, hit the solve button. When you’re ready, exit the building.
3.2 – Chelsea Tunnel
Make way to the Chelsea Tunnel, which is west of the Gotham Gazette. Head inside the tunnel and look to the left to find a fan protected by a chain link fence. Grapple to reach a broken section of the fence then follow the path through the tunnel, defeating the enemies along the way. When you reach the main level, examine the concrete wall to find Sample Drilling. Afterwards, climb up the elevator shaft to find 2 ore samples on a table. Examine them. Continue through the door and work your way to the extraction room. Examine the extraction machine with your AR then interact with the table next to the machine to start an investigation. Mark Composite Ore [10588-COS] and Sulfuric Acid to solve the investigation. Make your way to the exit to trigger a cutscene. Defeat all the enemies on the platform to trigger another cutscene then quickly flee the mines. When you reach topside, you’ll be messaged by Talia to meet up. Follow the objective nearby to find her on top of the CCNB building. After the cutscene, return to the Belfry!