To earn this trophy, you must do the following:
- In the sewers near the start of the game, pick the handgun up off the workbench.
- When in Norman's house, make sure that you do not leave the handgun behind on the gun rack.
- When you re-enter your basement at the end of the game (for the third time), after finding all the clues in the upper floors of the house, pick the handgun up off the floor.
- Then immediately go back upstairs and into the kitchen to the right.
- Interact with the kitchen table, and proceed when prompted.
For a full video guide, see the following: