Perhaps ironically, the most effective approach to extract information from someone may be kindness. In 2014, Swedish researchers compared a common, direct interrogation—where the questions are direct and specific—to the Scharff Technique, named after the highly successful German interrogator Hanns Scharff.
Scharff was not a typical Nazi interrogator. Unlike the infamous Klaus Barbie, he did not believe in using physical violence. Instead, Scharff got prisoners to spill their secrets through kindness and cunning.
“Judge a man by his questions rather than by his answers.” ― Voltaire
According to Pacific Standard magazine, he even used to share his wife’s baked goods with allied fighter pilots. Once, while strolling with a captured allied fighter pilot through the woords, Scharff claimed that American tracer bullets left a white instead of red smoke due to a chemical shortage, the pilot jumped in to correct him, saying the white smoke was a signal to pilots that they were low on ammo. Thus Scharff was armed with the information he sought. Contemporary researchers are now beginning to put his techniques to the test.
In the Swedish study, participants were given a story with 35 details and interrogated by phone, Scharff’s approach not only resulted in more (and more precise) information, but those being interrogated thought they gave up less information than they actually had, while those being interrogated directly felt they gave up more than they actually had. Kindness is not the only key ingredient to the Scharff Technique; having a “know-it-all” attitude compels information-disclosing corrections, as in the case of the pilot correcting his “friend.”
“The object of terrorism is terrorism. The object of oppression is oppression. The object of torture is torture. The object of murder is murder. The object of power is power. Now do you begin to understand me?” ― George Orwell, 1984
 Oleszkiewicz. S., Granhag. P.A., Montecinos. S.C. (2014) The Scharff-technique: eliciting intelligence from human sources.