The District statute establishing the Office of Citizen Complaint Review and its governing Citizen Complaint Review Board was enacted in 1999. In 2004, the office and the board body were renamed the Office of Police Complaints (OPC) and the Police Complaints Board (PCB).
The enabling statute for OPC can be found on the District of Columbia Official Code website. You can find the information under Title 5, Chapter 11, Subchapter 1. "Police Complaints Board; Office of Police Complaints."
The PCB and OPC were established on March 26, 1999 by the Council of the District of Columbia in the Office of Citizen Complaint Review Establishment Act of 1998. You can access the OPC regulations here.