Criminal courts frequently rely on accomplice witnesses (witnesses who testify regarding the role of an alleged co-conspirator in a crime) and jailhouse informants (witnesses who provide testimony based on information obtained while incarcerated) for prosecutorial information. Typically the testimony provided by such cooperating witnesses includes information garnered through the witnesses' conversations with the accused, which can include a purported confession to the crime.

Information from a cooperating witness is often provided in exchange for a reduced sentence or some other incentive. This kind of inducement creates a situation that is highly conducive to evidence fabrication on the part of the cooperating witness. In fact, one recent study concluded that lying informants are rarely prosecuted and therefore have much to gain and little to lose by testifying falsely.

While courts have recognized the unreliable nature of evidence obtained through bartered testimony, they have held that safeguards are in place to adequately protect the accused against a conviction based on false testimony. These safeguards allow effective cross-examination of a cooperating witness and enable the jury to consider a witness’s motivations. However, these safeguards do not always provide protection. There are cases in which prosecutors merely imply to cooperating witnesses that they will receive an incentive in exchange for testimony. In such cases, the exchange between prosecution and witness does not have to be disclosed to the jury.

In addition, psychological research on confession testimony—confessions obtained by investigators directly from the accused—reveal further problems with bartered testimony. This research indicates that jurors give undue weight to confession evidence when rendering guilt decisions. This effect is especially notable in cases where jurors are aware that a defendant has been offered an incentive in exchange for a confession. This is particularly relevant here because if people have difficulty realizing the effect that an incentive can have on a defendant’s behavior, they may also fail to realize the effect that an incentive may have on a cooperating witness’s behavior.

A common psychological phenomenon may account for jurors’ superficial examination of confession evidence. Studies show that people tend to explain the behavior of others in terms of internal dispositions or attitudes as opposed to external, situational factors. In one study, regardless of whether confession evidence was obtained via negative pressure (threats of worse treatment and/or harsher punishment) or positive pressure (promises of better treatment and/or leniency), mock jurors viewed a confession as evidence that the defendant committed the crime because “only a guilty person would confess to such a crime.” The same logic can be applied to the testimony of cooperating witnesses: jurors may presuppose that accomplice witnesses and jailhouse informants offer their testimony as atonement rather than deducing that external factors made it expedient to give the testimony.