law: Code of Criminal Procedure Act, 1973
  311.Power 
  
  to summon material witness, or examine person present.-
  Any Court may, 
  
  at any stage of any inquiry, trial or other proceeding under this Code, summon 
  
  any person as a witness, or examine any person in attendance, though not 
  
  summoned as a witness, or recall and re-examine any person already examined; and 
  
  the Court shall summon and examine or recall and re-examine any such person if 
  
  his evidence appears to it to be essential to the just decision of the case.