Massachusetts General Laws Part III. Courts, Judicial Officers and Proceedings in Civil Cases (Ch. 211-262) Ch. 233, § 25

If a witness or party whose testimony is wanted in a civil cause or proceeding pending in the commonwealth lives more than thirty miles from the place of trial, or is about to go out of the commonwealth and not to return in time for the trial, or is so ill, aged or infirm as to make it probable that he will not be able to attend at the trial, his deposition may be taken.