Mass. Gen. Laws ch. 262 § 53A
Any police officer named in section fifty and section fifty-three who attends as a witness at a place other than his residence in a criminal case pending in a district court, including the municipal court of the city of Boston, or in a juvenile court, or in the superior court shall be paid eight cents a mile for travel out and home for each day's attendance, except that travel allowance shall not be allowed when such travel is made in municipally-owned vehicles. Each officer shall certify in writing the amount of his travel and attendance. Such payments shall be in addition to his other expenses necessarily and actually incurred as provided for in section fifty and shall be paid in the same manner as such expenses are required to be paid by section fifty.
Mass. Gen. Laws ch. 262, § 53A