Good cop/bad cop

The "Good cop/bad cop" routine, also called Mutt and Jeff, joint questioning or friend and foe, is a psychological tactic used in negotiation and interrogation. "Good cop/bad cop" tactics involve a team of two interrogators who take apparently opposing approaches to the subject. The interrogators may interview the subject alternately or may confront the subject at the same time.
Technique.
The "bad cop" takes an aggressive, negative stance towards the subject, making blatant accusations, derogatory comments, threats, and in general creating antipathy with the subject. This sets the stage for the "good cop" to act sympathetically, appearing supportive and understanding, and in general showing sympathy for the subject. The good cop defends the subject from the bad cop. The subject may feel able to cooperate with the good cop, either out of trust or out of fear of the bad cop and may then seek protection by the good cop and provide the information the interrogators are seeking. The order can also be reversed. When performed in this manner, the good cop will try to gain a subject's trust. If that fails, the bad cop will intimidate the subject to make him crack under pressure.
The disadvantage of this technique is that it can be easily identified, and the "bad cop" may alienate the subject.