Massachusetts General Laws Part III. Courts, Judicial Officers and Proceedings in Civil Cases (Ch. 211-262) Ch. 233, § 46

If a person desires to perpetuate his own testimony or the testimony of another person, he shall apply in writing to two justices of the peace or notaries public, or a justice of the peace and a notary public, one of whom shall be an attorney at law, requesting them to take his deposition or the deposition of the person whose testimony he desires to perpetuate, and stating briefly and substantially his title, claim or interest in or to the subject relative to which he desires the evidence perpetuated, the names of all other persons interested or supposed to be interested therein and the name of the witness proposed to be examined.