Mass. Gen. Laws ch. 234A § 30A
If, by challenge or otherwise, a sufficient number of jurors duly drawn and summoned cannot be obtained for the trial of a case, the court shall cause jurors to be returned from the bystanders or from the county at large, to complete the panel, if there are on the jury not fewer than 7 of the jurors who were originally drawn and summoned.
Before causing additional jurors to be returned for service the jury pool officer shall file an affidavit with the court stating that more than the usual number of jurors are required on the case and that the jury pool has been exhausted. The judge sitting on the case shall make a finding as to the accuracy of said affidavit prior to the return of additional jurors.
The jurors from the bystanders shall be returned by the sheriff or the sheriff's deputy or by a disinterested person appointed by the court, and shall be qualified and liable to be drawn as jurors.
Mass. Gen. Laws ch. 234A, § 30A