The law is clear that a confession obtained by a promise of leniency or a threat of harm is inadmissible. Every interrogation manual knows this. The Reid technique's solution is elegant and is the subject of this chapter: communicate both, and say neither.
Saul Kassin and Karlyn McNall tested this directly in 1991. They gave participants transcripts of an interrogation that contained either minimization themes, maximization themes, an explicit offer of leniency, an explicit threat, or none of these. Then they asked what sentence the suspect could expect.
Participants who read the minimization transcript inferred leniency at levels comparable to the explicit promise. Participants who read the maximization transcript inferred harsher consequences comparable to the explicit threat. The message had been received in full. Nothing actionable had been said.
Minimization is the sympathetic register. The investigator suggests that the act was understandable, that anyone might have done it, that it was surely not planned, that the victim bears some responsibility, that this was a moment of weakness rather than a character. None of this is a promise about charges or sentence, and all of it communicates that a confession framed this way will be treated as a lesser thing.
Maximization is the opposite register and it usually carries a second payload: an assertion about evidence. We have your prints. A witness saw you. Your friend has already told us. In the United States, police may lawfully lie to suspects about evidence, and this permission is what makes the technique's most dangerous element possible — chapter 95 is about what a false evidence claim does to a person who knows they are innocent.
The mechanism that converts an implication into a confession is temporal discounting, and it is worth stating precisely because it explains something people find inexplicable from the outside.
Under high stress, in a room with no exit, after many hours, the value a person places on future outcomes collapses relative to immediate ones. The trial is abstract and months away. The interrogation is happening now and is unbearable now. The steepening of discounting under stress and fatigue is well documented, and it means the decision the suspect is actually making is not do I want to be convicted but do I want this to stop, with a background assumption — expressed by an enormous proportion of false confessors afterwards — that the truth would come out later.
It does not come out later. Kassin's research on the corruption effect shows that a confession, once obtained, contaminates everything downstream: witnesses change accounts to fit it, forensic examiners' interpretations shift, and juries convict despite contradictory evidence.
Which means the moment in the room, where the suspect trades a distant abstraction for immediate relief, is not a recoverable error. It is the case.
Cross-ref: Reid technique chapter above