law: Prevention of Corruption Act, 1988
  17. Persons authorized to investigate
  Notwithstanding anything contained in the Code
  
  of Criminal Procedure, 1973, no police officer below the rank,-
  (a) in the case of the Delhi Special Police
  
  Establishment, of an Inspector of Police;
  (b) in the metropolitan areas of Bombay,
  
  Calcutta, Madras and Ahmedabad and in any other metropolitan area notified as
  
  such under sub-section (1) of section 8 of the Code of Criminal Procedure,
  
  1973, of an Assistant Commissioner of Police;
  (c) elsewhere, of a Deputy Superintendent of
  
  Police or a police officer of equivalent rank, shall investigate any offence
  
  punishable under this Act without the order of a Metropolitan Magistrate or a
  
  Magistrate of the first class, as the case may be, or make any arrest therefor 
  
  without a warran
  Provided that if a police officer not below the
  
  rank of an Inspector of Police is authorized by the State Government in this
  
  behalf by general or special order, he may also investigate any such offence
  
  without the order of a Metropolitan Magistrate or a Magistrate of the first
  
  class, as the case may be, or make arrest therefor without a warrant:
  Provided further that an offence referred to in
  
  clause (e) of sub-section (1) of section 13 shall not be investigated without
  
  the older of a police officer not below the rank of a Superintendent of Police.