Here’s a sad idea:
The Authority discovered an abandoned underground laboratory. When they entered the facility, they discovered a sole inhabitant, a sentient worker robot. When interviewed, the robot revealed that they are an only person left after the workers and other robots are massacred. They don’t know how or why it happened.
Since the communication signal is unavailable and it cannot go outside due to them shutting down if they do so, the robot decided to spend their time doing manual labour like usual, including conserving what remains in the facility. This is a way for the robot to curb their loneliness.
Because of their conservating for roughly 50 years, the Authority managed to document bits and pieces of the facility while making speculations on how it happened. But due to the robot’s inability to go outside, they have to stay but also received visitors every once a week
The theme centered around loneliness and finding meaning in otherwise meaningless task. The horror is the vagueness of the massacre.
(account deleted)