The district attorney shall file vouchers with the auditor at the end of each fiscal year, and may file vouchers from time to time during the year, showing the disposition he has made of any money received from the special appropriation and the particular purpose for which it was spent. If at the end of the fiscal year a criminal proceeding is pending or under investigation, the vouchers as to any money spent in the proceeding or investigation need not be filed until the trial of the proceeding is ended or the investigation concluded.