Mass. Gen. Laws ch. 32 § 85
In any town which accepts this section prior to January first, nineteen hundred and sixty-two, or has accepted corresponding provisions of earlier laws by a two thirds vote at an annual town meeting the appropriate retirement board, established under section twenty, or if there is no such board, the selectmen, shall retire from active service and place upon the pension roll any permanent member of the police department and any permanent member of the fire department of such town found by it or them to be permanently incapacitated, mentally or physically, for useful service in the department to which he belongs, by injuries received through no fault of his own in the actual performance of his duty. Any permanent member of either of said departments who has performed faithful service therein for twenty-five years as aforesaid shall, at any time after attaining the age of sixty and before attaining the age of seventy, be retired at his request and shall, on attaining the age of seventy, be retired without any request on his part, and no other permanent member of either of said departments shall remain in service after he has attained or shall attain the age of seventy. If a permanent member of the police department of such a town was, prior to the establishment of a police department therein, employed in said town as a police officer by appointment under section ninety-six of chapter forty-one, the period of such appointment shall be counted as a part of his continuous service as a permanent member of its police department. Every person so retired shall annually receive from the town as a pension a sum equal to one half of the annual compensation received by him at his retirement. The selectmen may in an emergency call upon any person so pensioned for such temporary service in the department from which he was retired as they may deem him fitted to perform, and during such service he shall be entitled to full pay.
Mass. Gen. Laws ch. 32, § 85