Good cop/bad cop, also called 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.
The "bad cop" takes an aggressive, negative stance towards the subject, making blatant accusations, derogatory comments, threats, and in general creating antipathy between the subject and himself. 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 will also defend the subject from the bad cop. The subject may feel they can cooperate with the good cop either out of trust or out of fear of the bad cop. They may then seek protection by and trust the good cop and provide the information the interrogators are seeking.
The technique has disadvantages in that it can be an obvious tactic and the "bad cop" may alienate the subject.