While paused I moved the item (a panoptic pillar II) that a disguised thief (Boggyman) was about to try and steal/look at, at the same time I clicked on the 'reveal thief' button.
After unpausing the guest is now stuck, they will only move from their location if bumped due to changing the nearby rooms, deleting the building does not fix the behaviour.
The reveal thief button is greyed out and their needs have all dropped to minimum apart from environment and entertainment. Placing cameras and security guards nearby does not appear to detect the thief.

I know he is a thief due to 0 Buzz/knowledge and not having the 'bought a ticket' entry in his event log