Mass. R. Sup. Jud. Ct. 2:12
(Applicable to criminal cases.)
The court need not entertain any motion for postponement, grounded on the want of material testimony, unless supported by an affidavit, which shall state (1) the name, and, if known, the residence, of the witness whose testimony is wanted, (2) the particular testimony which he is expected to give, with the grounds of such expectation, and (3) the endeavors and means that have been used to procure his attendance or deposition; to the end that the court may judge whether due diligence has been used for that purpose. The party objecting to the postponement shall not be allowed to contradict the statement of what the absent witness is expected to testify, but may disprove any other fact stated in such affidavit. Such motion will not ordinarily be granted if the adverse party will admit that the absent witness would, if present, testify as stated in the affidavit, and will agree that the same shall be received and considered as evidence at the trial or hearing, as though the witness were present and so testified; and such agreement shall be in writing, upon the affidavit, and signed by such adverse party or his attorney. The same rule shall apply, mutatis mutandis, when the motion is grounded on the want of any material document, thing, or other evidence. In all cases the granting or denial of a motion for postponement shall be discretionary, whether the foregoing provisions have been complied with or not.
Mass. R. Sup. Jud. Ct. 2:12