Using the authorities, the town guard, or local lord in a fantasy setting, the police or government in modern-day or sci-fi, is another way of isolating your characters and cutting them off from help.
You can go further, telling the police may be informing the villain of how much the characters have learned. It is also an avenue the villain may use to manipulate the characters.
The local authorities may be involved because someone high up has been seduced or controlled, maybe it is to protect themselves or the community.
Maybe the villain has already ‘won’ and the government is trying to cover it up?
This can cross the line from a specific horror, to a conspiracy.
The Body Snatcher books and films played on this. As time passed, the alien ‘pods’ replaced more real people with alien facsimiles, leaving fewer people for the protagonists to turn to, and less people they could trust.