The Central Criminal Division was actually only addressed as such internally, among the staff of police system, while the outsiders called it the Criminal Investigation Department. It represented the highest command post out of all of the entire investigation departments.
Their department mainly dealt with government affairs. Generally, the investigation unit of each local police station would be in charge whenever there were any criminal cases present. However, when more serious cases arose, they had to get involved and take responsibility.
As the Criminal Division didn't have any frontline staff members, they would form a Special Investigation Group each year, which was tasked to investigate these major above-mentioned cases.