CORDY, J.

On June 28, 2007, a grand jury indicted the defendants, two Boston College students, Daniel Carr and John Sherman, on charges that they trafficked in cocaine over fourteen grams, possessed psilocybin with intent to distribute, and possessed marijuana with intent to distribute, following discovery of the illegal drugs in their campus dormitory room. On December 17, 2007, Carr filed a motion to suppress the drugs and other evidence seized as a result of a warrantless search. Sherman filed a similar motion and a motion to suppress his statements to the college police. After an evidentiary hearing, the judge granted the defendants' motions to suppress.

On interlocutory appeal, the Appeals Court reversed. Commonwealth v. Carr, 76 Mass.App.Ct. 41 (2009). We granted the defendants' application for further appellate review to consider the Commonwealth's challenge to the judge's findings that the initial warrantless entry into the room by Boston College police officers was unlawful, and that the defendants did not voluntarily consent to the subsequent search of their room. We conclude that the judge did not err in finding that the Commonwealth failed to satisfy its burden of proving the voluntary consent of the defendants to search their room. We affirm. Because the drugs and other evidence will be suppressed, we need not decide whether the initial entry into the room was lawful.2

1. Background. The following facts are drawn from the judge's findings and the uncontested testimony at the motion hearing. Around midnight on February 14, 2007, Sergeant John Derick of the Boston College police department received a telephone call from April Wynn, resident director of Gonzaga Hall on the Boston College campus. Wynn told Sergeant Derick that she had received a report from two students that a "weapon" was inside a room in Gonzaga Hall. Wynn brought the two students to the campus police station, and they told Sergeant Derick that Daniel Carr had been bullying students and bragging about having a knife. The students stated that there was a third student, who wished to remain anonymous, who reported seeing the butt of a gun, possibly a toy gun, inside Carr's room.

Sergeant Derick, along with Sergeant Anthony Cadogan and Officer Sean Daley, met with Wynn and another resident director, Austin Ash, in Wynn's office. The three officers and two resident directors then proceeded to Carr's room. The officers were all uniformed and armed. Sergeant Derick knocked on the door and announced himself as a Boston College police officer. A male voice inside the room stated, "Hold on, I've got to put my pants on." Sergeant Derick knocked again after approximately thirty seconds had elapsed, and the door was opened. Sergeant Derick entered the room and the other two officers remained just outside the doorway. There were three young men in the room.

Sergeant Derick asked who lived in the room. One of the men, later identified as Zachary Taylor, stated that he did not live in the room and Sergeant Derick told him to leave. After Taylor left the room, Sergeant Derick told Carr and Sherman that he had received an anonymous report of a gun or weapon in the room. Carr stated that he had a "fake" gun but had thrown it out. Sergeant Derick then read Carr his Miranda rights and asked him where the gun was. Carr said, "I think it's under the bed" and pointed to the bed. Sergeant Derick reached under the bed and retrieved what looked like a .45 caliber handgun, but, on closer inspection, proved to be a replica gun that may have been capable of shooting a projectile. The other two officers then entered the room and Sergeant Derick asked the students if there were more weapons in the room. Sherman produced and handed over a folding knife. A smaller knife was later found in a desk drawer and a kubotan, a martial arts weapon, was also recovered.

Based on his experience, Sergeant Derick believed that there could be more weapons in the room and told the defendants he wanted to search the entire room. Sergeant Cadogan handed each of the defendants a form that contained two parts: the top half, a "Miranda waiver," contained text and a line for a signature; the bottom half, "consent to search," also contained text, and had a line at the bottom that did not indicate whether it was for a signature.3 Carr asked if he could make a telephone call and was allowed to do so. Carr telephoned his father, who then spoke with Sergeant Derick, telling him, "It's just a cap gun ... a toy gun. What's the big deal?" Each defendant filled out the form, signing the Miranda waiver, but neither defendant placed a signature on the "consent to search" half of the form.

Sergeant Cadogan and Officer Daley conducted a full search of the room while Sergeant Derick stepped out of the room to update Wynn and Ash. During the course of the search, Officer Daley found a bag of psilocybin mushrooms and a bag of marijuana. The defendants were then asked to step into the hallway and were placed under arrest. Subsequently, twelve bags of a white powdery substance were found in a jacket that both defendants said belonged to Taylor.4 Two additional bags containing white powder were found under the beds. There was a footlocker in the middle of the room that contained a locked box smelling of marijuana. The officers found a key in a desk drawer and opened the box, which contained ten marijuana cigarettes, rolling papers, seeds, and the defendants' passports. The officers also found a marijuana pipe and a piece of paper listing names and amounts of money.

2. Motion to suppress. In reviewing the grant or denial of a motion to suppress, we accept the judge's subsidiary findings of fact absent clear error, Commonwealth v. Yesilciman, 406 Mass. 736, 743 (1990), and accord "substantial deference" to the judge's ultimate findings. Commonwealth v. Monteiro, 396 Mass. 123, 131 (1985), citing Commonwealth v. Doucette, 391 Mass. 443, 447 (1984). "On a motion to suppress, `[t]he determination of the weight and credibility of the testimony is the function and responsibility of the judge who saw the witnesses, and not [the appellate] court.'" Commonwealth v. Yesilciman, supra, quoting Commonwealth v. Moon, 380 Mass. 751, 756 (1980). "The clear error standard is a very limited form of review.... Where there has been conflicting testimony as to a particular event or series of events, a judge's resolution of such conflicting testimony invariably will be accepted." Commonwealth v. Yesilciman, supra, quoting Commonwealth v. Spagnolo, 17 Mass.App.Ct. 516, 517-518 (1984). A "trial judge's ruling on a motion to suppress may be reversed where the facts found are clearly erroneous or `where justice requires [that the appellate court] substitute its judgment for that of a trial judge at the final stage.'" Commonwealth v. Spagnolo, supra at 517, quoting Commonwealth v. Moon, supra. "The ultimate legal conclusions to be drawn from the subsidiary findings of fact, however, are matters for review by this court." Commonwealth v. Robinson, 399 Mass. 209, 215 (1987).

a. Consent. "When the police rely on consent to justify a warrantless [search], under both the Fourth Amendment [to the United States Constitution] and art. 14 [of the Massachusetts Declaration of Rights], the prosecution `has the burden of proving that the consent was, in fact, freely and voluntarily given.'" Commonwealth v. Rogers, 444 Mass. 234, 237 (2005), quoting Bumper v. North Carolina, 391 U.S. 543, 548 (1968). "[T]he Commonwealth must provide us with more than an ambiguous set of facts that leaves us guessing about the meaning of this interaction and, ultimately, the occupant's words or actions.... If either the officer's request or the occupant's response is so ambiguous that we are unable to discern whether the occupant voluntarily consented to [the search], our inquiry will be over and the entry must be deemed unlawful." (Citations omitted.) Commonwealth v. Rogers, supra at 238-239.

The judge found that the Commonwealth had not established that the defendants gave consent to search their room. She based this finding on what she described as "discrepant" testimony and what she found to be "equivocat[ion]" in Sergeant Cadogan's testimony. The evidence presented to the judge supports this finding.5

Sergeant Derick's only testimony on the subject was that after he stated that he would like to search the room, he "asked that they fill out the consent to search," and the defendants were handed the forms. Sergeant Cadogan testified that after Sergeant Derick said he wanted to search the room, the defendants were each given a form, and "[t]hey just filled it out." When asked if there was any verbal response, Sergeant Cadogan first stated that there was none, but on redirect examination then stated that they said, "yes."6 On cross-examination, Sergeant Cadogan again stated that "one of them said something." When given his original report from the incident to refresh his memory, Sergeant Cadogan then stated that it was his testimony that he did not hear a verbal response from either defendant.7 Officer Daley testified that Carr "stated yes" when Sergeant Derick asked if they could search the room. He also testified that he asked Sherman if they could search his part of the room and Sherman "stated yes" and began to fill out the form. However, on cross-examination by Sherman's counsel, Officer Daley stated that when he asked Sherman to fill out the form, Sherman began to fill out the form, and that was the extent of the conversation.

The judge was not persuaded that there was consent to the search based on the forms that were partially filled out by the defendants. After reviewing the forms, it is clear that both defendants placed their signature on the Miranda waiver portion of the form, but neither placed a signature on the half that gives consent to search. In sum, the evidence before the judge as to consent was equivocal and supported her conclusion that the Commonwealth had not met its burden.

b. Voluntariness of consent. In addition to finding that the Commonwealth had not satisfied its burden of proving actual consent, the judge went on to say that, even if she was able to "determine clearly that either defendant had given consent to search, there were coercive aspects to the officers' exercise of authority that would vitiate a finding of voluntariness." "The question whether consent was voluntary is a question of fact to be determined in the circumstances of each case, with the burden of proof on the government." Commonwealth v. Aguiar, 370 Mass. 490, 496 (1976). The Commonwealth must prove "consent unfettered by coercion, express or implied, and also something more than mere `acquiescence to a claim of lawful authority.'" Commonwealth v. Walker, 370 Mass. 548, 555, cert. denied, 429 U.S. 943 (1976), quoting Bumper v. North Carolina, 391 U.S. 543, 549 (1968). While no factor by itself is conclusive, factors to consider include, but are not limited to: the presence of armed, uniformed officers; whether the defendant was informed of his right to refuse consent; the age, intelligence, and other personal characteristics of the defendant; and whether the defendant was in custody when consent was given. See Commonwealth v. Sanna, 424 Mass. 92, 97-98 n.10 (1997); Commonwealth v. Harmond, 376 Mass. 557, 561-562 (1978).

The judge's ultimate conclusion that the Commonwealth had not proved voluntary consent was supported by her subsidiary findings that: (1) "[Sergeant] Derick immediately demanded the occupants' identities and ordered Taylor to leave; thus, his very first acts had a compulsory dimension to them"; (2) the "armed officers completely blocked the only exit[,] and the two resident directors [stood] in the hallway[, lending] further institutional presence"; (3) "[Sergeant] Derick signaled his distrust of the defendants"; and (4) Sergeant Derick's "pronouncement, `I would like to search the room,' sounded more like an order than a request."8 The judge found that "an objective person would not have felt able to refuse the officer's request or leave the room." Each of her subsidiary findings were in turn based on testimony adduced at the hearing.

The Appeals Court concluded "as a matter of ... independent judgment that the facts and circumstances establish that the consent was free and voluntary and neither coerced nor mere acquiescence to a claim of lawful authority." Commonwealth v. Carr, 76 Mass.App.Ct. 41, 52 (2009). Because a finding of voluntariness is a question of fact, it should not be reversed absent clear error by the judge. Commonwealth v. Yesilciman, 406 Mass. 736, 743 (1990). "So long as the judge's account is plausible in light of the entire record, an appellate court should decline to reverse it. `Where there are two permissible views of the evidence, the factfinder's choice between them cannot be clearly erroneous.'" Demoulas v. Demoulas Super Mkts., Inc., 424 Mass. 501, 510 (1997), quoting Gallagher v. Taylor, 26 Mass.App.Ct. 876, 881 (1989).

The judge was in the best position to assess the weight and credibility of the testimony given at the motion hearing. Although the Appeals Court reviewed the evidence presented and concluded that consent was voluntarily given, its alternate view of the facts and circumstances does not indicate clear error on the part of the judge, and we find none.9

3. Conclusion. The Commonwealth failed to satisfy its burden to prove that consent was freely and voluntarily given; therefore, we affirm the judge's order allowing suppression of the drugs and other evidence seized in an illegal search of the defendants' room.

So ordered.