He tricked the junta by teling them that as Khanh had played a large part in putting down the 1960 revolt, Thi would be an ideal mechanism for keeping the disliked Khanh in check.
He tricked the junta by teling them that as Khanh had played a large part in putting down the 1960 coup attempt, Thi would still be harboring resentment. According to Mau, Thi would thus be an ideal mechanism for keeping the disliked Khanh in check.