Section 703. Employment of counsel

With the written approval of the county
  judge of a county in which an indictment has been found for a capital or
  other crime which presents unusual difficulty upon  the  trial  thereof,
  the  district attorney may employ counsel to assist him upon such trial.
  Such approval shall be filed in the office  of  the  county  clerk.  The
  board  of  supervisors  shall audit as other county charges a reasonable
  compensation and the necessary expenses of such counsel as certified  by
  the presiding judge or justice.