The Garda National Bureau of Criminal Investigation consists mainly of detectives, who are generally senior investigators, and is headed by an officer of Detective Chief Superintendent rank. The head of the Garda NBCI reports to the Assistant Commissioner in charge of Special Crime Operations, who reports directly to the Garda Commissioner. The NBCI was established on January 21, 1997, centralising other investigative branches around the country, as a response to the proliferation of serious and organised crime. Its predecessor was the Garda Central Detective Unit (CDU). Its main function is to provide a specialist investigative response to serious criminal activity, supporting other Garda units and/or local investigators in their investigation into serious crimes. The NBCI is the main unit within the Gardaí that investigates internal Garda criminality and corruption.