"'Justice' is people getting what they deserve," Harris said. "And 'mercy' is people getting what they need -- not what they want, not what they deserve -- but what they need."
It's a masterful technique -- since no matter what the subject chooses, admitting a need for either justice or mercy is in itself a big step towards admitting guilt.
Harris has anticipated Paolilla's response -- "mercy." He then follows up, saying, "I'd like to be able to understand why."
A short little while later Paolilla makes a dubious statement; that her boyfriend forced her to shoot her friends.
"I had made the gun go off. Not purposely, though," she tells Harris's partner.
The jury didn't buy it and Paolilla was sentenced to life in prison.
But even when he pressures suspects with the facts, Harris can't always get a confession in person.
In the case of James McCann, the man brought in and accused of killing his estranged wife, Hattie Faye, Harris must wait patiently. It takes an initial hour-long interrogation, then hours of polygraph testing days later, to get McCann, in what looks like an act of conscience, to confess.
"He decided to write me an apology letter and describe what happened," tells Harris. Harris read the note to "Primetime Crime," "I am very sorry I've not been honest," it reads.
In a second interrogation conducted one week after the first, McCann explains that he, "Got one of those pillows and I was just gonna put it over her face and scare her...I guess I lost [track of] time."
There is little denying the importance of a non-coercive interrogation that passes muster with a judge.
"In a courtroom, when a jury sees a defendant sitting there, trying to say he wasn't part of something and the next thing here you have a tape or a videotape or a written confession and the person is admitting to the act that they're trying to now deny," Harris says, "There's nothing more damning."
The innocent have little to fear in the interrogation room, Harris says, but the guilty have more to fear in this masterful game of cat and mouse.
"If you've done something and you think that you're smarter than us? We've been doing this a long time," explains Harris. "You're gonna talk to me."