Actually, I've been wondering all along whether they put him there a) to eavesdrop on what the "detainees" would say to someone they thought was "one of them", and b) so they could trace who/what/how/where he passed along the information.
Think how valuable it would be to find out who the prisoners were trying to sneak messages to, and how. It would provide a new motherlode of leads to follow to the terrorists' nests.
Yup. I think this is closer to whats really going on. It wouldn't suprise me to find out that Captain Yee is a CIA mole. (but, we'll never know)