(Applicable to District Court and Superior Court)
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.
This rule is based upon former G.L. c. 276, § 39 (Rev.St.  c. 135, § 14) which was applicable to the District Court.
The power of a judge to control the progress and, within the limits of the adversary system, the shape of a trial, is universally held to include the broad discretionary power to sequester witnesses before, during, and after their testimony. Geders v. United States , 425 U.S. 80 (1976); Holder v. United States , 150 U.S. 91, 92 (1893); United States v. Robinson , 502 F.2d 894 (7th Cir.1974); United States v. Eastwood , 489 F.2d 818, 821 (5th Cir.1973); Commonwealth v. Dougan , 377 Mass. 303 (1979); Commonwealth v. Watkins , 373 Mass. 849 (1977); Commonwealth v. Vanderpool , 367 Mass. 743 (1975); Commonwealth v. Blackburn , 354 Mass. 200 (1968); Commonwealth v. Follansbee , 155 Mass. 274 (1892); Commonwealth v. Parry , 1 Mass.App. Ct. 730, 736, (1974).
Although sequestration may be well used to prevent the occurrence of perjury, it serves an equally important function in preventing one witness' testimony from being inadvertently molded by the testimony of other witnesses. “The process of sequestration consists merely in preventing one prospective witness from being taught by hearing another's testimony....” 6 J. WIGMORE EVIDENCE § 1838 at 461 (Chadbourne rev. 1976). It additionally aids in detecting testimony which is less than candid, see WIGMORE, supra, and prevents improper attempts during recess to influence the witness' testimony in light of that already given. Geders v. United States, supra, at 87.
Since the sequestration of witnesses is within the discretion of the judge, the judge may order that only some of the witnesses be removed from the courtroom or kept separated. In Commonwealth v. Therrien , 359 Mass. 500 (1971), it was held proper for the trial judge to except from a general order of sequestration one witness deemed “essential to the management of the case.” Id. at 508.
In conformity with prior practice, the court is to have discretionary power to exclude the testimony of a witness who remains in court in violation of a court order. In Commonwealth v. Crowley , 168 Mass. 121 (1897), a witness called by the defendant to impeach the testimony of a prosecution witness was not allowed to testify because he had remained in court in violation of a court order. Although at the time of the court order the defense had not intended to use that witness at trial, the exclusion of his testimony was upheld because during the progress of the trial it became apparent that he might be called for impeachment purposes. Conversely, the court may receive the testimony of a witness who is present at trial in violation of a sequestration order. Commonwealth v. Shagoury , 6 Mass. App. Ct. 584 (1978); Commonwealth v. Hall , 86 Mass. (4 Allen) 305, 306 (1862). In addition, a trial judge may revoke or modify a previous sequestration order. Commonwealth v. Parry , 1 Mass.App. Ct. 730, 736 (1974). The rule by its terms is inapplicable to a defendant. A sequestration order would affect a defendant quite differently from the way it affects a non-party witness, because of the defendant's need to consult with counsel. Geders v. United States, supra, at 88.