Massachusetts General Laws Part IV. Crimes, Punishments and Proceedings in Criminal Cases (Ch. 263-280) Ch. 269, § 4

If any persons who are so riotously or unlawfully assembled, and who have been commanded to disperse, as before provided, refuse or neglect to disperse without unnecessary delay, any two of the magistrates or officers before mentioned may require the aid of a sufficient number of persons, in arms or otherwise as may be necessary, and shall proceed, in such manner as they deem expedient, forthwith to disperse and suppress such assembly, and seize and secure the persons composing the same, so that they may be proceeded with according to law.