Mass. Gen. Laws ch. 111B, § 12

The commonwealth, the several counties, cities and towns, subject to appropriation, may establish service forces to perform the function of the police in accordance with the provisions of section eight. Such service forces may be a part of a police department, the department, or may be a separate unit. Members of the force shall be trained to carry out the responsibilities of police, and other individuals as these are set out in section eight, including the administration of first aid to intoxicated persons in need of medical assistance.