law: 43.Officers competent to investigate offences under Chapters IV and VI.-
  Notwithstandinganything contained in the Code, no police officer,-
  (a) in the case of the Delhi Special Police Establishment, constituted under sub-section (1) of section 2 of the Delhi Special Police Establishment Act, 1946 (25 of 1946), 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 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 Chapter IV or VI.