The background for carrying out this research is that there is a rationale for legal claims in order to determine a legal subject of a Witness to be the legal subject of a Defendant directly by the Panel of Judges in an ongoing criminal justice process for criminal acts of corruption, in order to carry out justice or law enforcement more effectively and efficiently, so that substantive justice can be achieved in law enforcement. The methods that have been used in this research are legal actions that allow a Witness legal subject to become a legal subject for the Defendant directly by the Panel of Judges in an ongoing judicial process, normative juridical approach legal research or research that examines legal rules according to library research, and the research specifications are analytical descriptive, and in this research secondary data was obtained. The data collection technique was carried out through literature study, and the data analysis used was qualitative and explained descriptively. This research concludes that in the existing criminal justice system, the legal subject of the Witness can actually be the legal subject of the Defendant in an ongoing trial; it's just that such "determination" is not made explicitly. To determine a witness as a defendant, there are two parties who can take the initiative to determine the witness directly as a defendant in a trial process at a corruption criminal court. Namely the Public Prosecutor, especially the KPK Public Prosecutor. Carried out at the request of the Public Prosecutor to the Panel of Judges.