MANDAMUS IS A PROPER REMEDY WHEN RESOLUTION OF PUBLIC RESPONDENT IS TAINTED WITH GRAVE ABUSE OF DISCRETION:

     The writ of mandamus is not available to control discretion neither may it be issued to compel the exercise of discretion. Truly, it is a matter of discretion on the part of the prosecutor to determine which persons appear responsible for the commission of a crime. However, the moment he finds one to be so liable it becomes his inescapable duty to charge him therewith and to prosecute him for the same. In such a situation, the rule loses its discretionary character and becomes mandatory. (METROPOLITAN BANK and TRUST COMPANY vs. ROGELIO REYNADO and JOSE C. ADRANDEA, G.R. No. 164538, August 9, 2010, DEL CASTILLO, J.).