Mass. R. Evid. 615
At a party's request, the court may order witnesses excluded so that they cannot hear other witnesses' testimony. Or the court may do so on its own. But the court may not exclude any parties in a civil proceeding, nor the defendant in a criminal proceeding.
Mass. Guid. Evid. 615
This section is derived from Zambarano v. Massachusetts Turnpike Auth., 350 Mass. 485, 487 (1966), and Mass. R. Crim. P. 21 ("Upon his own motion or the motion of either party, the judge may, prior to or during the examination of a witness, order any witness or witnesses other than the defendant to be excluded from the courtroom."). See Commonwealth v. Therrien, 359 Mass. 500, 508 (1971) (court may except from general sequestration order a witness deemed "essential to the management of the case").
"Sequestration of witnesses lies in the discretion of the trial judge." Zambarano, 350 Mass. at 487. See Commonwealth v. Herndon, 475 Mass. 324, 336 (2016) (trial judge properly found that defendant's sister's Facebook posts were sufficiently relevant to justify naming her as potential witness subject to sequestration order, and that adding her to witness list was not pretext to exclude her from courtroom); Commonwealth v. Perez, 405 Mass. 339, 343 (1989) (court has discretion to exempt police officer in charge of investigation from sequestration order). Upon a violation of a sequestration order, a trial judge has discretion in taking remedial action. See, e.g., Commonwealth v. Neves, 474 Mass. 355, 367-368 (2016) (no abuse of discretion in denying motion to strike testimony of witness who had violated sequestration order where defense counsel stated he was "satisfied" with judge's "instructional remedy" to jury); Custody of a Minor (No. 2), 392 Mass. 719, 726 (1984) (trial judge may exclude testimony of person who violates sequestration order); Commonwealth v. Navarro, 2 Mass. App. Ct. 214, 223 (1974) ("but even in a case where a violation of sequestration order is wilful a trial judge might for good reason prefer to invoke contempt proceedings rather than declare a mistrial").
The third sentence of this section is derived from the Sixth and Fourteenth Amendments to the United States Constitution, and Article 12 of the Declaration of Rights of the Massachusetts Constitution. See also Commonwealth v. Nwachukwu, 65 Mass. App. Ct. 112, 117-120 (2005). Civil litigants also have a right to be present during the trial. See White v. White, 40 Mass. App. Ct. 132, 141-142 (1996).