The Hitman disguised himself as a mild-mannered accountant interested in Desert Jack's Graboid Tour. In actuality he was a hit man out for Frank who had lost a very important key. It is thought that he shot and killed Frank.
The Hitman served as a convenient way to spirit Frank off stage and tie up the loose ends for the episode.
|"Damned jeep trail gets worse every year" ―Earl Bassett[src]|