Massachusetts General Laws Part III. Courts, Judicial Officers and Proceedings in Civil Cases (Ch. 211-262) Ch. 248, § 25

This chapter shall not affect the power of the supreme judicial court, or the superior court, or a justice thereof, to issue a writ of habeas corpus in its discretion, and thereupon grant bail to a person for whatever cause he has been committed or restrained, or to discharge him as law and justice require. The court shall have no power to issue a writ of habeas corpus, at its discretion for--a person who has been committed by the governor and council, the senate, or the house of representatives in the manner and for the causes mentioned in the constitution, or a person who is imprisoned or restrained of his liberty pursuant to a criminal conviction.

This chapter shall not affect the power of any court or magistrate to issue a writ of habeas corpus, when necessary to bring before it a prisoner for trial in a pending criminal case; or to bring a prisoner to be examined as a witness in a suit or proceeding, civil or criminal, pending before the court, if the personal attendance and examination of the witness is necessary for the attainment of justice.