Thank you for such kind words!
All the sounds come from a website called Freesound.org. I had bigger plans for the intruder, but time constraints prevented them from being implemented. To unlock good ending you have to kill all phantoms using camera and shoot the intruder (Note that shooting the pistol ends the game). Shooting an intruder in the head is impossible due to the inaccurate size of the collider. Thank you for your detailed feedback!