Mental health professionals have shown increasing involvement in providing expert testimony regarding a defendant's capacity to waive legal rights before and during an interrogation. In the 1966 Supreme Court case of Miranda v. Arizona, the Court ruled that any statement arising from a custodial interrogation of a suspect would be presumed to be involuntary and not admissible unless the suspect is informed of his rights to remain silent, to avoid self‐incrimination, to obtain legal counsel before and during police questioning, and to obtain free legal counsel if indigent. This waiver of rights must be made knowingly, intelligently, and voluntarily. A comprehensive psychological evaluation of a defendant's capacity to have waived the rights at the time of police questioning provides the trier of fact useful information in determining the admissibility of a confession. The standard protocol for most evaluations functionally integrates a defendant's capacities with the legally relevant criteria espoused by Miranda and subsequent case law. The evaluation is comprised of a comprehensive clinical interview, psychological testing, including the use of specialized assessment procedures, and a review of third‐party data.

Confessions are a key piece of evidence to be used against a suspect in courtroom proceedings. Defense attorneys often attempt to suppress the confession at the pretrial stage by raising issues of an involuntary Miranda waiver or an involuntary confession. At trial, the credibility of a defendant's statements to the police becomes an important issue. The interrogation of a highly suggestible suspect heightens the risk of false or less than accurate confession. Mental health testimony is often useful to the trier of fact at both the pretrial and the trial stages. A comprehensive psychological assessment in this context includes the use of the Gudjonsson Suggestibility Scales to supplement clinical interview information, third party data, and other psychological tests. An individual's interrogative suggestibility is influenced by age, intelligence, memory, sleep deprivation, anxiety, and previous criminal convictions.