I flew with an F/O at DAL who was a special agent in OAK during his furlough. He wasn't flying, just a special agent. He said the job was interesting, but the hours were killing him. It was tough to have a home life. He was glad to come back to DAL. He had some great stories.
When I was in the military, we did some flying on behalf of various law enforcement agencies. It was ungodly boring.