.Notwithstanding anything contained in the Code, no police officer,

(a) in the case of the Delhi Special Police Establishment, below the rank of a Deputy Superintendent of Police or a police officer of equivalent rank;

(b) in the metropolitan areas of Mumbai, Kolkata, Chennai and Ahmedabad and any other metropolitan area notified as such under sub-section (1) of section 8 of the Code, below the rank of an Assistant Commissioner of Police;

(c) in any other case not relatable to clause (a) or clause (b), below the rank of a Deputy Superintendent of Police or a police officer of an equivalent rank, shall investigate any offence punishable under this Act.