It's possible with some wards, or Necromancy. Magic meant to bind the dead. [Though, he may know it via video games.] It's evil. Probably the worst thing you can do to a soul. The dead earned their rest.

[Her jaw clenches, and she has to look away, a shimmering wave of heat beginning to surround her.] Merlin told me that the jailer said the people there were lowering company profits. That's why they were imprisoned. I...didn't get to ask the ghost myself. I was already gone.