The Sixth Amendment guarantees, in relevant part, that "[i]n all criminal prosecutions, the accused shall enjoy the right to a . . . public trial." U.S. Const. Amend. VI.
A defendant has a constitutional right to a trial - including jury selection - that is open to the public. See Presley v. Georgia, 130 S. Ct. 721, 724 (2010), citing Press-Enterprise Co. v. Superior Court of Cal., 464 U.S. 501, 505 (1984), and Waller v. Georgia, 467 U.S. 39, 46 (1984) (“the Sixth Amendment right to a public trial extends to the voir dire of prospective jurors”). “The guarantee of a public trial is for the benefit of the defendant; a trial is far more likely to be fair when the watchful eye of the public is present.” Owens v. United States, 483 F.3d 48, 61 (1st Cir. 2007), citing In re Oliver, 333 U.S. 257, 270 (1948) (“The knowledge that every criminal trial is subject to contemporaneous review in the forum of public opinion is an effective restraint on possible abuse of judicial power.”). The “sure knowledge that anyone is free to attend gives assurance that established procedures are being followed and that deviations will become known.” Press-Enterprise, 464 U.S. at 508.
The public trial guarantee has been considered so important that courts have reversed convictions or granted habeas relief where the courtroom was closed for the announcement of the verdict, United States v. Canady, 126 F.3d 352, 364 (2nd Cir. 1997), where a trial inadvertently ran so late one night that the public was unable to attend, Walton v. Briley, 361 F.3d 431, 433 (7th Cir. 2004), and where the trial was closed for the testimony of just one witness, United States v. Thunder, 438 F.3d 866, 868 (8th Cir. 2006).
“Thus, courts recognize a strong presumption in favor of a public trial.” Commonwealth v. Cohen (No. 1), 456 Mass. 94, 105 (2010), quoting Commonwealth v. Baran, 74 Mass. App. Ct. 256, 296 (2009). See Press-Enterprise I, 464 U.S. at 509 (“trial closures are to be “rare and only for cause shown that outweighs the value of openness”).
Where a judge wishes to close the courtroom for a portion of a criminal trial, she “must make a case-specific determination that closure is necessary.” Cohen, 456 Mass. at 107, citing Globe Newspaper Co. v. Superior Court, 457 U.S. 596, 608 (1982).
That determination must satisfy four requirements articulated by the Supreme Court:
"‘ the party seeking to close the hearing must advance an overriding interest that is likely to be prejudiced,  the closure must be no broader than necessary to protect that interest,  the trial court must consider reasonable alternatives to closing the proceeding, and  it must make findings adequate to support the closure.'"
Cohen, 456 Mass. at 107, quoting Waller, 467 U.S. at 48.
Violation of the public trial right “is a structural error and not susceptible to harmless error analysis.” Cohen, 456 Mass. at 105, quoting Baran, 74 Mass. App. Ct. at 296, quoting Baran, 74 Mass. App. Ct. at 296. See also United States v. González-López, 126 S. Ct. 2557, 2564 n. 4 (2006) (citing Waller, 467 U.S. at 49 n. 9, for the proposition that “violation of the public-trial guarantee is not subject to harmlessness review”); Owens, 483 F.3d at 63, quoting Judd v. Haley, 250 F.3d 1308, 1315 (11th Cir. 2001) (“Once a petitioner demonstrates a violation of his Sixth Amendment right to a public trial, he need not show that the violation prejudiced him in any way. The mere demonstration that his right to a public trial was violated entitles a petitioner to relief.”).
A defendant's right to a public trial “keep[s] his triers keenly alive to a sense of their responsibility” and “encourages witnesses to come forward and discourages perjury.” Waller, 467 U.S. at 46. “[J]udges, lawyers, witnesses, and jurors will perform their respective functions more responsibly in an open court than in secret proceedings.” Estes v. Texas, 381 U.S. 532, 588 (1965) (Harlan, J., concurring).
The First Circuit has noted the potential prejudice arising from closure of trial to the public during jury selection:
"It is possible that jurors might have been more forthcoming about biases and past experiences if they had faced the public. It is also possible that [the defendant] and the Government might have picked a more impartial jury or asked different questions with local citizenry watching. All of these possibilities call into question the fundamental fairness of [the defendant’s] trial. Requiring that [the defendant] prove any of them by a preponderance of the evidence would be a burden impossible to meet."
Owens, 483 F.3d at 65, citing González-López, 126 S. Ct. at 2565 (refusing to apply harmlessness review to violation of right to counsel because “[w]e would have to speculate upon what matters the rejected counsel would have handled differently - or indeed, would have handled the same but with the benefit of a more jury - pleasing courtroom style or a longstanding relationship of trust with the prosecutors. And then we would have to speculate upon what effect those different choices or different intangibles might have had.”).