Joe Navarro is a former FBI agent and nonverbal communications expert. In this Wired video, he describes how FBI agents interrogate people.
The first thing FBI agents do is calm the suspect. Navarro says he did this by using a vocal tone that was "lower and slower." FBI agents seat suspects next to the door and they don't sit too close to them. They also avoid too much eye contact and take slow deep breaths, which the suspect will subconsciously mimic, making them relax.
FBI agents start by asking simple questions as a way to get the suspect to start talking. That creates a connection with the interrogator and makes it more likely the suspect will answer tougher questions to follow.
He also says there are no real "tells" like nose touching. Instead, agents look for levels of "discomfort and distress" to help them determine whether or not an interrogation subject is lying or not. "We're not looking for deception, because there is no single behavior indicative of deception."