Collaborators of justice or cooperating witnesses in organized crime cases are often reluctant to testify about their knowledge. Such reluctance can be due to fear to become involved, or due to an unwillingness to incriminate themselves. The Organized Crime Convention asks States parties to "consider providing for the possibility, in accordance with fundamental principles of its domestic law, of granting immunity from prosecution to a person who provides substantial cooperation in the investigation or prosecution of an offence covered by this Convention" (article 26, para. 3) (UNODC, 2012).
The purpose for granting witnesses immunity from prosecution in exchange for testimony is to make it easier to prosecute higher echelon criminals through the testimony of less important figures. The legal balance is similar to that for the mitigation of punishment: what is an appropriate accommodation to excuse a criminal for misconduct in exchange for information needed to prosecute a more important or serious criminal?
When considering the issue of immunity from prosecution, the scope of its application is a central concern. In most countries where immunity is given, the immunity is conditional or confined in some way (UNODC, 2008). For example, there may be a requirement that the cooperation given reflects honestly held views (even if the information turns out to be incorrect), or a requirement of a link between the crime for which immunity is granted and the crime about which the suspect testifies. The conditions for immunity may depend on the value of the suspect's evidence provided and its actual impact. The actual impact could include e.g., stopping or preventing a crime from occurring. In many cases, the immunity is transactional, meaning that leniency in sentencing is provided if truthful and complete testimony is given.
Witness immunity has been criticized due to potential misuse by the prosecutor. For example, immunity may be provided to witnesses as a mere "fishing expedition" to obtain information without a clear idea of the specific individuals or crimes suspected. An overzealous prosecutor might use the incriminating testimony improperly in a subsequent case (and implicate the previously immunized witness) without any systematic oversight of his or her actions (Sheptycki, 2017; Woislaw, 2015-16).
There are other problems raised by witness immunity. In some countries, immunity provides no protection from civil suits against witnesses who incriminate themselves. Therefore, a person might be held liable for damages and compensation from an injured party, even though no criminal prosecution can result from their testimony. It can also be argued that the use of testimony that is the result of inducements, such as immunity, is questionable. These testimonies can be seen as coerced or tainted, making it less convincing to judges or juries at trial. In addition, this type of testimony can possibly lead to erroneous convictions of wrongfully accused defendants, when prosecutors, judges, or juries accept the false or incorrect testimony of an immunized witness as fact.
Witness immunity also has benefits for the criminal justice system. For the offences characteristic of transnational organized crime, there are often few alternatives to obtaining evidence of organized crime from reluctant witnesses.
Procedural safeguards exist in many jurisdictions to ensure that testimonies are not either self-serving to the witness or false. For example, cross-examination of witnesses at trial, and the need for corroboration of certain types of evidence, serve as a check on accuracy. Another safeguard is that the need for granting immunity must be demonstrated by the prosecution in most jurisdictions, indicating that the testimony is necessary to the public interest and that the information cannot be obtained voluntarily, or in another way (Flanagan, 1980-81; Sheptycki, 2017; Trott, 2017). In addition, in case in which witnesses are found to lie, they can be prosecuted for perjury (i.e. lying under oath in an official proceeding).
Witness immunity is designed to balance the interests of the public in prosecuting high-level offenders with the interests of the witness. Restrictions on the use of witness immunity are designed to accomplish this balance.