This article is devoted to the characteristics of the Polish model of the institution of key witnesses and the actual experience of its use since its introduction into the Polish legislation in 1998. In addition to organizational measures such as the establishment of the Central Bureau of Investigation of the National Police Headquarters, this has become one of the main instruments of criminal law used to combat the most serious crime, particularly organized crime. The introduction of a formula of absolute discharge for people involved in the offence in exchange for cooperation with law enforcement and justice and the disclosure of other offenders has become a necessity in the face of an explosion of crime after the collapse of communism in 1989 and as a result of the partial ineffectiveness of the existing methods of law enforcement. After a few years, the development of these social ills began to threaten the stability and internal security of the state. But it should be stressed emphatically that under Polish law and the rules of criminal law key witness is no “magic formula” which overturns the regulations, or is it a form of evidence which merits special weight. Polish law does not provide for a legal theory of evidence. The fact that someone is a “Crown” witness has a real, formal importance onlyto his personal situation and the substantive process, and his life (the suspension of criminal proceedings against him and ultimately a release for him from criminal responsibility, as well as the material support of the state and protection from retaliation from other criminals). The key witness is an ordinary witness within the meaning of the term as defined by the importance of his account, while the actual substantive significance of his evidence to the establishment of the truth may only result from the credibility of his evidence combined with the professional approach of all participants in the criminal proceedings and the use of all necessary tools of a fair criminal trial resulting in proper judgment on the merits of the case.