Everyone knows good cop/bad cop; one of the most memorable moments of the first season of the Wire involved Bodie goading Detective Carter into attacking him during an interrogation, before mocking him with “You’re supposed to be the good cop!”
Of course, that’s fiction, and a new study published in Legal and Criminal Psychology suggests that good cop/bad cop may not even work that well.
Over one hundred university students and staff in the UK took part in the experiment. Half had to describe a real job they once had, and half had to describe a fake experience. Both groups told their stories to interviewers, and members of the lying group stood to earn £5 if they managed to carry their lie.
During questioning, subjects faced two interviewers. The first was a female who asked questions in a neutral voice. The second, a male, took notes. The second interviewer either adopted a positive demeanour (i.e., smiling and nodding), a neutral demeanour, or a negative one.
Truth tellers gave more detailed answers than the liars—but only in the presence of a positive second interviewer. By being reassuring, the interviewers not only provoked a more detailed story from the truth-tellers, they were able to contrast that against the liars.
Incidentally, a positive presence also changed the liar’s behaviour: they said more negative things about their fictional boss.
So, if and when you’re trying to suss out a liar, perhaps strike a more receptive tone—people telling the truth will speak up, leaving the liars out in the cold.