On FIVE there's an easy way to kill the Pentagon Thief. This only works with 2 or 4 players.

First go downstairs on the very botom floor and turn the on the power. Then run back upstairs at the very top.

After that get on the middle table and wait until the zombies are all dead.

Next wait for the Pentagon Thief to come. If the Pentagon Thief is after someone that person has to stay on the table, while the other people simply knife him to death!