Traditionally confessions have been considered the gold standard of evidence creating an almost irrebuttable proof of the defendant's guilt.This began to change in the 1800's when the U.S. Supreme Court first began to question strong-handed interrogation tactics: “the presumption upon which weight is given to [confessions], namely, that one who is innocent will not imperil his safety or prejudice his interests by an untrue statement.” 
It wasn't until 1936 that the Supreme Court determined that involuntary confessions were abhorrent to the Due Process Clause of the 14th Amendmement of the U.S. Constitution. Confessions which are involuntary may be excluded from evidence unless the defendant opens the door to the admission of the confession. Recent studies have demonstrated that false confessions are a real and ever present threat to fair adjudication of criminal cases.
The exclusion of involuntary evidence is premised on three principals: First, exclusion of involuntary confessions tends to deter police misconduct. Second, a confession should be freely made by a rational person. Finally, confessions obtained with duress are inherently unreliable.
Voluntariness is determined by a factfinder (judge or jury) by examining and taking into consideration the totality of the circumstances..
Factors may include objective factors such as:
- Duration of the interrogation
- Length of pre-trial detention
- Place and conditions of interrogation
- Psychological threats
- Police conduct during interrogation
- Whether force or threat of force was used during interrogation
Similarly, the factfinder must examine the defendant's subjective state of mind to determine whether given all those factors, the confessions was, in fact, involuntary. In doing so, they should consider the defendant's physical and mental characteristics: age, race, education, history and psychological state of mind during the interrogation.
Deception alone is usually not enough to warrant exclusion of a confession as involuntary. In Frazier v. Cupp , the U.S. Supreme Court upheld the admissibility of a confession when the police falsely told the defendant that his cousin had confessed to the crime. The court held that deception was just one factor in the voluntariness test and that deception in and of itself was not dispositive.
In certain circumstances, police misconduct may be so egregious that the confession evidence should be excluded without regard for how that conduct the defendant.
- Hopt. v. Utah, 120 U.S. 430 (1887)
- Brown v. Mississippi, 297 U.S. 278 (1936)
- Haynes v. Washington, 373 U.S. 503 (1963)
- Frazier v. Cupp, 394 U.S. 731 (1969)