Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 12, § 18

If there is no assistant district attorney, the district attorney may employ a clerk to aid him; and in the northern, eastern, middle, Norfolk, Plymouth, Berkshire, Hampden and northwestern districts, the district attorney may appoint, for the sitting at which the appointment is made, a competent person to act as an assistant to the district attorney. The compensation of any person employed or appointed hereunder shall be paid by the commonwealth.