Botsford, J.
The defendant, Jerome McNulty, appeals from his conviction of murder in the first degree, G. L. c. 265, § 1, as well as from two convictions of assault and battery by means of a dangerous weapon (a knife), G. L. c. 265, § 15A.1 He also appeals from the denial of his motion for a new trial. We conclude that the defendant’s right under art. 12 of the Massachusetts Declaration of Rights to be informed by the police of his attorney’s attempts to provide assistance was violated. See Commonwealth v. Mavredakis, 430 Mass. 848, 859-860 (2000) (Mavredakis). We further conclude that the error in admitting in evidence the defendant’s entire, signed statement to the police was not harmless beyond a reasonable doubt in relation to the conviction of murder in the first degree. We therefore reverse that conviction and remand that portion of the case for a new trial. We affirm the convictions of assault and battery by means of a dangerous weapon, but remand for sentencing.
1. Procedural background. Before trial, the defendant moved to suppress the statement he made to the police during a custodial interrogation following his arrest, claiming violations of the Fifth, Sixth, and Fourteenth Amendments to the United States Constitution, and art. 12. After an evidentiary hearing, a judge in the Superior Court (motion judge) denied the motion. The defendant was tried before a jury and another Superior Court judge (trial judge) in February, 2004. He filed a timely notice of appeal from his convictions and, while his direct appeal was pending, he filed a motion in this court seeking a new trial. We remanded the motion to the Superior Court for disposition. On December 7, 2007, after a nonevidentiary hearing, the trial judge denied the motion; the judge also denied the defendant’s motion for discovery of police procedures. The defendant filed [307]*307a timely notice of appeal from the denial of these posttrial motions, and that appeal has been consolidated with his direct appeal from his convictions.
2. Factual background, a. Death of Linda Correia and injuries to AlexSandra Correia and Heather Colaban. We summarize facts that the jury could have found at trial, leaving recitation of other facts for discussion in connection with the issues raised on appeal. On March 28, 2001, Linda Correia was one of the defendant’s girl friends. She lived in a second-floor apartment in Salem with her two children, AlexSandra, aged ten, and Edward, aged eight; her sister, Maureen; Maureen’s children, Tatiana, aged six, and Adriana, aged four; and Maureen’s friend, Heather Colaban.2 The defendant lived in Lynn with Lisa Bowen, his “baby’s mother,” but frequently stayed overnight in Linda’s bedroom.
On the night of March 28, after Maureen left for her 11 p.m. to 7 a.m. work shift, present in the apartment were Colaban; Colaban’s boy friend, Georgie Sanchez; Maureen’s boy friend, Gustavo “Black” Reyes; three of the children, AlexSandra, Tatiana, and Adriana (Edward was not present); Linda; and the defendant. The latter two were in Linda’s room “bagging” marijuana and cocaine. At 5:30 a.m. the next morning, March 29, Maureen telephoned to wake Sanchez and Reyes, who were starting new jobs with a temporary employment agency, and both men left the apartment at about 5:45 a.m.
Shortly before 7 a.m., Colaban woke to the sound of “banging” coming from Linda’s bedroom. When the noise became louder, she banged on Linda’s door, and heard Linda faintly scream and cry, “Help me. He’s trying to kill me.” Colaban was unable to open the locked door. The noise also woke Alex-Sandra. She retrieved a butter knife and tried to open the lock with it (something she had previously done), but was unsuccessful. Colaban continued to bang on Linda’s bedroom door and screamed, “Open the door. Do you want me to call the police? Let me in.”
At that point, the defendant unlocked the door, and came out [308]*308of the room wearing a blood-soaked shirt and holding a black-handled knife. His face was expressionless. He slashed Colaban in the face and in the area of her back and upper shoulders, slashed AlexSandra in her upper thigh, and then went into the kitchen. Colaban ran from the apartment seeking assistance, and telephoned the police.3
Both before and after the defendant left Linda’s room, Alex-Sandra heard her mother crying and calling for help. Holding her cousin Tatiana (Adriana remained asleep), she looked into the bedroom and saw her mother’s foot on the floor. After the defendant left the apartment through the back door, located in the kitchen, AlexSandra shut the back door, inserting knives into it to keep it closed. She then went into her mother’s bedroom, finding her lying on her back. There was blood on her body and on the carpet. Linda was conscious, and again asked for help. AlexSandra stayed for a few seconds, then went to the kitchen and took the telephone from Tatiana, who had just dialed 911.4 When emergency personnel arrived, Linda was still conscious.
The responding police officers found a “flip knife” and two other knives in the bedroom; two knives outside Linda’s bedroom; and a knife just outside the apartment, on the threshold of the front door. Other knives also were found on the kitchen floor, or had been used to wedge the kitchen door shut.
After leaving the apartment, the defendant, covered with blood, walked down the street and entered the premises of the temporary employment agency through which Sanchez and Reyes had just begun employment. He told the manager that he had just been mugged, and wanted a taxicab. Instead of sitting down, however, the defendant lay on the floor, below the level of the windows. The manager became suspicious, and told the defendant to wait outside. When he heard sirens, the defendant pulled up his hood and walked away from Linda’s apartment. The manager alerted a police officer in a cruiser, and the defendant was apprehended soon thereafter.
Linda was taken to a hospital. She underwent surgery in an [309]*309attempt to repair the wounds to her neck, but died about ten hours after surgery. She had been stabbed or cut eleven times, including four times on the left side of her neck, and had four defensive “cutting wounds” on her left hand, left arm, and left shoulder. She also had multiple bruises. Ultimately, she died as the result of blood loss from the destruction of blood vessels, in particular the carotid artery, jugular vein, and anterior thyroid artery.
b. The defendant’s custodial statement,5 Following the defendant’s arrest shortly after 7 a.m. on March 29, 2001, he was taken to the Salem police station for booking. All his clothing was seized during the booking process, and he was given a blanket to wear. The defendant was read Miranda rights within fifteen minutes of arriving at the station, and again around 9 a.m., when he agreed to speak to Sergeant Dennis Marks of the State police and Detective James Page of the Salem police.
During the interview, Marks wrote down the defendant’s words as he spoke. According to the defendant’s statement as memorialized by Marks, at about 5:50 a.m. on March 29, the defendant spoke with Sanchez and Reyes in the apartment kitchen, and told them he was going to visit his mother in a hospital. When he returned to Linda’s bedroom, he lay down on the bed and the two started talking. Linda seemed to be “aggravated mad,” and got progressively louder and angrier. She got up, pulled a black bag or pocketbook from under the bed, and took out a “ball like white package.” The defendant thought it was cocaine, but vigorously declined Linda’s offer to give him some. Linda snorted the cocaine using a card.
The defendant then left the room, went to the kitchen to get a soda, and returned. When he got back, Linda was “a different person,” and apologized to him. Then, as he sat on the end of the bed and began dressing, she started hitting him, “like a clinging hit,” and then asked him to hold her. At that point, she reached over his shoulder and stabbed the night table beside the bed with a knife “like a butterfly with a dragon on it.” She [310]*310then started swinging the knife at him. Once, she caught him in the hand and he fell, grabbing a blanket. Linda ended up on top of him, and it seemed to him as though she was trying to stab him. They rolled off the bed onto the floor, the blanket was tangled “everywhere,” and Linda screamed when they fell. There was a lot of blood, the defendant was not sure whether it came from him or her, and Linda continued to wrestle with him.
When the defendant got up to leave, Linda had another knife, and she “jump[ed] up” and continued to try to wrestle. He heard Colaban knock on the door, and Linda told Colaban to “get out, run, leave, like I was doing something to Linda.” When the defendant opened the door, Colaban had a kitchen knife in her hand, yelling at him to leave. Linda came out of the room swinging a knife, and Colaban was pointing a knife at his chest and face. He “smacked” the knife out of Colaban’s hand, then saw AlexSandra and Tatiana in the living room and told them to telephone 911. The defendant walked through the kitchen and left through the back door of the apartment to call for help. He went into the temporary employment agency and asked them to call an ambulance. Then, he heard sirens and went outside to look for the police.
After a fifteen-minute break in the custodial interview, the defendant further told the police that he had not smoked marijuana the night before and did not “do” cocaine. He stated he had drunk five or six ounces of rum the previous night, which just made him tired but had no other effect. He denied having had a knife in his hand and denied knowing how the drugs he was carrying when arrested came into his possession, but stated that they were in the same container that Linda had taken from under the mattress in her room.
c. The defendant’s testimony at trial. The defendant testified at trial. His account of what happened on the night of March 28 into the morning of March 29 was similar to the statement he gave the police, except that he testified that during the night he was using cocaine, smoking marijuana “blunts,” and drinking quite heavily. He also testified that, in reaction to Linda’s use of knives, he swung wildly, afraid for his life. While he did not remember slashing or stabbing any of the three victims, he agreed that he must have done so.
[311]*311d. The defendant’s experts’ testimony. The defendant called two expert witnesses to testify concerning his posttraumatic stress disorder (PTSD) and its impact on his behavior on the early morning of March 29, 2001. Dr. Charles Debring, a neuropsychologist, testified generally about PTSD as a disorder recognized in the Diagnostic and Statistical Manual of the American Psychiatric Association (DSM-IV) and affecting some people who have experienced significant traumatic events. Debring described clusters of PTSD symptoms, including reexperiencing the trauma, avoidance, and hyperarousal in reaction to a perception of danger. He also testified about a series of psychological tests he had administered to the defendant. He opined that the pattern shown by the defendant’s test results were typical or consistent with PTSD. The second witness, Dr. Robert Joss, a forensic psychologist, had interviewed the defendant on three separate occasions. Joss opined that the defendant had PTSD, stemming from a childhood trauma the defendant experienced when his best friend was kidnapped and murdered as a child, and that the defendant would overreact to a threat such as someone threatening him with a knife, with the consequence that he would engage in “flight or fright [sic] behavior” lacking rational control. Joss further opined on the effect of the defendant’s PTSD:
“[H]e over perceived the threat [from Linda] that may have been there, acted in a manner to extricate himself as best he could and in so doing caused her death. And then in his extrication from the apartment, he was confronted with two individuals who were between him and the exit.”
2. Claimed violation of right to assistance of counsel, a. Additional background. The defendant challenges on appeal the denial of his motion to suppress his statement to Sergeant Marks and Detective Page. In his motion, he claimed that the police had obtained his statement in violation of his right to the assistance of counsel protected by art. 12 as interpreted in Mavredakis, 430 Mass, at 859-861, and also that his statement was not voluntary. We summarize the motion judge’s findings of fact regarding the claimed Mavredakis error, according them deference absent clear error, and referring to other evidence as necessary to provide [312]*312context for the discussion.6 We make constitutional assessments based on those facts independently. Commonwealth v. Diaz, 453 Mass. 266, 272 (2009).
At approximately 9:12 a.m. on March 29, 2001, the defendant’s custodial interview with Sergeant Marks and Detective Page began. Before the interview, the defendant again was read Miranda rights, and was asked to acknowledge whether he understood the rights. Marks wrote down the defendant’s statements as he spoke. The group took a break from approximately 10 a.m. until 10:15 a.m., during which time the defendant was given a soda and a cigarette. The interview resumed at 10:15 a.m.
At 10:27 a.m., Attorney Raymond Buso was appointed by the Committee for Public Counsel Services to represent the defendant and began driving from the South Boston Division of the Boston Municipal Court Department to the Salem police station. According to Buso’s telephone records, Buso telephoned the Salem police station at 10:31 a.m.,7 and identified himself as the defendant’s attorney. Officer Patricia Murphy, who answered the telephone, neither confirmed nor denied the defendant’s presence, even though she had been the booking officer. Murphy transferred Buso’s call into Detective Sergeant Prosniewski’s voice mail. Prosniewski was the public information officer for the police department. Buso telephoned the police department a second time at 10:34 a.m., after disconnecting from Prosniewski’s voice mail, reached Murphy, and explained to her that he needed to speak to a “live body.” Murphy transferred him to Officer Baglioni. Baglioni was acquainted with Buso. Although Baglioni confirmed the defendant was at the station, he told Buso that he needed to speak to Sergeant Griffin, and gave Buso a different telephone number. Over the next four or five minutes, Buso attempted to reach that number. When he eventually got through to Griffin at 10:42 a.m., he identified himself as counsel for the defendant and told Griffin that he wanted to speak with his client. Griffin confirmed that the defendant was at the station, but told Buso that he could not speak to the defendant at that [313]*313time. Buso asked Griffin “to tell the defendant not to talk to the police and that he would be there shortly”; Griffin said, “O.K.” Before relaying any message, however, Griffin called the first assistant district attorney. Griffin was advised to inform the defendant that counsel had been appointed and wanted to speak to him, and that the defendant could end the interview and speak to counsel if he wanted to.
At approximately 10:45 a.m., Griffin relayed this message to Marks and Page outside the interview room. By this time, the defendant had finished his statement and the officers were reviewing it with him. Marks told the defendant that Buso had been appointed to represent him; that the defendant could stop speaking to the officers and speak to Attorney Buso at that time or could keep speaking to them; and that it was his choice. The defendant stated that he wished to keep speaking to the officers. Marks memorialized what he had conveyed to the defendant about counsel on the piece of paper on which he was writing the defendant’s statement and, at 10:52 a.m., the defendant acknowledged through his signature “that the statement accurately reflected what he had been told concerning Attorney Buso.” Between 10:52 a.m. and 11 a.m., Marks read the entire statement to the defendant. At approximately 11 a.m., the defendant signed each page of Marks’s handwritten notes, acknowledging the written words were his statement.
Buso arrived at the Salem police station about 11 a.m. He identified himself as counsel for the defendant, and asked to speak to the defendant “right away.” About three or four minutes later, Griffin met with Buso. Although Buso asked to speak with the defendant, Griffin denied the request, stating that “he had informed [the defendant] that an attorney had called and that he had passed the message on that I asked him to, and that [the defendant] wished to continue talking.” It was not until about twenty minutes after his arrival at the police station that Buso was permitted to speak to the defendant, which was about fifty minutes from the time he had first contacted the Salem police department. The motion judge found that while the police should have been “more aggressive” in responding to Buso’s inquiries, the police had not been “purposefully dilatory.”
Based on these findings, the motion judge ruled that Sergeant [314]*314Griffin was obligated, once he had spoken to Buso at 10:42 a.m., to inform the defendant immediately of Buso’s attempts to offer assistance, rather than contacting the first assistant district attorney. See Commonwealth v. Vao Sok, 435 Mass. 743, 753 (2002). The judge, however, concluded that the information conveyed to the defendant at 10:45 a.m. about Buso’s appointment and availability satisfied the requirements of Mavredakis. Accordingly, the judge concluded that because nothing of substance transpired between 10:42 a.m. and 10:45 a.m., the error did not prejudice the defendant and did not require suppression of any part of the statement. The judge denied the defendant’s motion to suppress.8
b. Analysis. In Mavredakis, this court held that under art. 12, when an attorney representing a suspect held in custody makes it known to the police that the attorney is seeking to reach his or her client to provide legal advice, the police have an affirmative duty to inform the suspect immediately of the attorney’s efforts. Mavredakis, supra at 859-860. Failure to do so ordinarily requires suppression of statements made by a defendant thereafter, because the prior waiver becomes “ ‘inoperative’ for further admissions.” Id. at 861, quoting Commonwealth v. McKenna, 355 Mass. 313, 324 (1969). The principles outlined in Mavredakis have been part of our law for many years. See Commonwealth v. Sherman, 389 Mass. 287, 296 (1983) (police failure to inform defendant of attorney’s request to be present “vitiated the defendant’s waiver of his Miranda rights”); Commonwealth v. McKenna, supra at 323-324 (police failure to inform defendant of attorney’s request to be present during [315]*315interrogation rendered any previous Miranda waiver by defendant “inoperative”). See also Commonwealth v. Mahnke, 368 Mass. 662, 691-693 (1975), cert, denied, 425 U.S. 959 (1976) (statements made after police knew defendant’s attorney urgently sought to contact principal police officer on case, but did not so inform defendant, properly suppressed as part of prosecution’s case-in-chief; statements could be used to impeach defendant if he testified).9
The duty to inform described in Mavredakis is one that attaches immediately after the attorney communicates to the police that he or she represents a suspect in police custody and seeks to communicate with the suspect in order to provide legal advice. See Mavredakis, 430 Mass, at 852, 861-862 (defendant’s statements made any time after 10:15 p.m., when defendant’s first attorney telephoned police station and asked to speak to defendant, should have been suppressed); Commonwealth v. McKenna, 355 Mass, at 324-325. See also Commonwealth v. Vao Sok, 435 Mass, at 751, 753 (“when an attorney identifies himself or herself to the police as counsel acting on a suspect’s behalf, art. 12 requires the police to stop their questioning and inform the suspect of the attorney’s availability immediately”; improper for police lieutenant first to contact assistant district attorney about attorney’s attempts to assist defendant rather than directly informing defendant of attempts, but in circumstances of case, error harmless beyond reasonable doubt). Accordingly, in the present case, the failure of the police to inform the defendant of Buso’s telephone call immediately after Murphy received Buso’s original call at 10:31 a.m. was improper; the trial judge, in deciding the defendant’s motion for a new trial, correctly ruled that all state[316]*316ments made by the defendant after 10:31 a.m. should have been suppressed. We also agree with the trial judge that, in the particular circumstances of this case, where there was no way to determine from Sergeant Marks’s handwritten memorialization of the defendant’s statement exactly what the defendant said between 10:15 a.m. and 10:31 a.m., and what he said between 10:31 a.m. and 10:45 a.m., every statement of the defendant memorialized between 10:15 a.m. and 10:45 a.m. was subject to suppression.
That there was a duty to inform the defendant concerning Buso’s efforts to contact him as of 10:31 a.m. leaves open the question what information the police were required to convey. Both the motion judge and the trial judge, in deciding the defendant’s motion to suppress and motion for a new trial respectively, concluded that the information conveyed by Marks to the defendant about Buso’s message satisfied Mavredakis and that the defendant, in stating at some point between 10:45 a.m. and 10:52 a.m. that he would continue to speak with the police after hearing Marks’s information, validly waived his right to the assistance of counsel. We disagree.
The obligation, defined in Mavredakis, is “to apprise the defendant of a specific communication from his attorney that bore directly on the right to counsel.” Mavredakis, supra at 861, quoting State v. Stoddard, 206 Conn. 157, 169 (1988). Here, according to the motion judge’s findings, Buso made four separate points to the Salem police when he ultimately was connected to Sergeant Griffin: (1) he represented the defendant; (2) he wanted to speak to the defendant; (3) the police were to tell the defendant that Buso said not to talk to the police; and (4) Buso would be at the station shortly. In our view, each of Buso’s four points related directly to the defendant’s right to counsel, see id., and the police here essentially failed to inform the defendant of three out of the four. In particular, as Mavredakis makes clear, the statements that Buso had expressly requested to speak to the defendant and would be at the station “shortly” — the second and fourth points — could be of critical importance in “actualizing” the abstract promise of an attorney provided by the Miranda warning into concrete reality; there is a significant difference between being told that one can stop questioning and speak to an appointed attorney, and hearing that the appointed attorney has [317]*317already stated that he or she wants to meet and speak, and is in fact due to arrive at one’s side “shortly.” See Mavredakis, supra at 859-860.10’11
The third point was also significant — that is, it was critical for the defendant to be told, which he was not, of the specific advice that the identified attorney, Buso, was already giving — namely, that the defendant should not continue to speak to the police. See Commonwealth v. Vao Sok, 435 Mass, at 752-753 (in concluding that defendant was adequately informed of his attorney’s efforts to render legal assistance, court noted that State police officer informed defendant that defendant’s attorney had indicated he [attorney] wanted ongoing polygraph examination terminated, that he was seeking to locate defendant on behalf of another attorney already representing defendant on another case, and that he wanted all questioning of defendant to cease). See also Commonwealth v. Anderson, 448 Mass. 548, 552, 556 (2007) (if investigating State police lieutenant had not informed defendant that identified attorney had been appointed to represent him and that attorney had requested defendant not be interviewed, defendant’s waiver of assistance of counsel would not have been valid under art. 12 and Mavredakis). While the police are not required to “deliver verbatim to a defendant the message given by his attorney,” Commonwealth v. Vao Sok, supra at 752, Buso’s particular message — not to talk to the [318]*318police — fell within the duty to inform because it “bore directly on the right to counsel.” Mavredakis, supra at 861.12
In sum, we conclude that, because the police did not convey adequately to the defendant the substance of his attorney’s telephone message and advice, the defendant’s subsequent indication that he would continue to speak to the police did not constitute a knowing or intelligent waiver of the Miranda rights. See id. As a result, evidence of all “postbreak” statements made and actions taken by the defendant in connection with the police interrogation — that is, all statements and actions from 10:15 a.m. until the conclusion of the interview at 11 a.m., including the defendant’s signing every page of the statement —• should have been suppressed. See Commonwealth v. McKenna, 355 Mass, at 324-325.
Where, as here, the defendant properly objected to the admission of his statement on Mavredakis grounds, and the Mavredakis errors at issue are constitutionally based, the question we now must confront is whether the admission of the postbreak portions of the statement at trial was harmless beyond a reasonable doubt. See Commonwealth v. Vao Sok, supra at 753 (preserved Mavredakis violations subject to analysis under harmless beyond reasonable doubt standard).13 See also Commonwealth v. Tyree, 455 Mass. 676, 701 (2010), quoting Commonwealth v. [319]*319Rios, 412 Mass. 208, 214 (1992) (“We have recognized that a constitutional violation gives rise to presumptive prejudice that can be overcome only where the Commonwealth makes an ‘affirmative showing’ of harmlessness beyond a reasonable doubt”). To answer the question, “we analyze the case to see whether the error might have had an effect on the jury or contributed to the verdicts, and whether the Commonwealth’s evidence was ‘ “merely cumulative” of evidence properly before the jury,’ ... or was overwhelming without the erroneously admitted evidence.” Commonwealth v. Dagraca, 447 Mass. 546, 553 (2006), quoting Commonwealth v. Sinnott, 399 Mass. 863, 872 n.8 (1987). See Commonwealth v. Vasquez, 456 Mass. 350, 361 (2010), quoting Sullivan v. Louisiana, 508 U.S. 275, 279 (1993) (“The inquiry ‘is not whether, in a trial that occurred without the error, a guilty verdict would surely have been rendered, but whether the guilty verdict actually rendered in this trial was surely unattributable to the error’ ”).
(i) Murder conviction. As to the conviction of murder in the first degree, we cannot say the error was harmless beyond a reasonable doubt under this standard.
This court has delineated a number of factors that bear on the determination whether a trial error involving improperly admitted evidence is harmless beyond a reasonable doubt.14 The [320]*320factors include “(1) the relationship between the evidence and the premise of the defense; (2) who introduced the issue at trial; (3) the weight or quantum of evidence of guilt; (4) the frequency of the reference; and (5) the availability or effect of curative instructions.” Commonwealth v. Mahdi, 388 Mass. 679, 696-697 (1983). See Commonwealth v. Dagraca, 447 Mass, at 553 (adding to Mahdi factors “the importance of the evidence in the prosecution’s case”).
We begin with the connection between the improper evidence and the premise of the defense. That premise was that while the defendant did in fact kill Linda, in doing so, he did not have the capacity to act with the requisite malice for murder because of his PTSD, and his actions showed he was acting either in lawful self-defense or, at worst, in a manner constituting voluntary manslaughter. The defendant’s full statement to the police, however, sets out a version of what happened in the early morning hours of March 29 that clearly could be found to conflict with much of the physical evidence in the case relative to Linda, as well as the testimony of all the other witnesses present in and outside the apartment at the time. Moreover, as a result of the conflict, the jury could view the statement as depicting a man who intentionally, and falsely, was seeking to create a picture [321]*321of himself as the victim of the violence of others or at least one who had minimal responsibility for the violence that had taken place.
It is true that much of the substance of this self-serving depiction was contained in the prebreak portion of the statement about which Sergeant Marks permissibly could have testified. However, by signing his name to each page of Marks’s notes, the defendant effectively adopted the notes in their entirety as his own written “statement.” This act, which occurred during the postbreak period, had a number of consequences. First, the presence of the defendant’s signature on each page could be understood to add a considered, deliberative quality to the defendant’s statement, particularly because the jury could find (based on Marks’s testimony) that the defendant only signed each page after the break, after he had “chosen” not to speak to his lawyer, and after he had listened to Marks read the entire statement out loud to him and agreed that it was indeed his statement. The impression that this act could have confirmed was that the defendant’s statement was far from a hasty or pressured response to police interrogation, but was instead a considered, thought-out version of events that the defendant wanted to convey.
Second, because of the presence of the defendant’s signatures, Marks’s writing was admitted in evidence as a trial exhibit, and Marks was permitted to read it verbatim to the jury. See Commonwealth v. Pina, 342 Mass. 472, 473 (1961). Without the signatures, neither could have occurred. Rather, the Commonwealth would have been confined to introducing Marks’s oral testimony about what the defendant had told the police during the prebreak portion of the March 29 interview; the notes themselves would have remained in their untransformed state as simply Marks’s notes and, as such, inadmissible. See Commonwealth v. Beaulieu, 333 Mass. 640, 649 (1956). Cf. Commonwealth v. Brum, 438 Mass. 103, 114 (2002). Instead, the jurors were provided the complete statement — prebreak, post-break and the portion indicating the defendant was rejecting the assistance of an attorney — in documentary form. We have recognized “the exceptionally potent quality of a defendant’s statement or confession,” Commonwealth v. DiGiambattista, 442 Mass. 423, 447 (2004), and also that the “potency can only [322]*322be magnified when the evidence of that statement or confession is presented by one or more of the interrogating officers.” Id. The jury here not only heard Marks read the defendant’s complete statement word for word, but they were able to review and discuss together every detail of the statement as closely as they chose during their deliberations because it was before them in the form of an exhibit. One may reasonably surmise that jurors are likely to give greater weight to a written document than oral testimony on the same subject, for which they must rely on their memories. See State v. Beckley, 157 Vt. 446, 450 (1991), quoting People v. Mims, 204 Ill. App. 3d 87, 93 (1990) (although testimony regarding substance of defendant’s confession would be admissible, if defendant’s signature on typed confession was “tainted” by improper police promises, document should not be admitted in evidence; “we are concerned by the ‘undue weight that jurors may accord the written word, especially when they must rely on their memories alone when considering the oral testimony’ ”). Cf. Commonwealth v. Avila, 454 Mass. 744, 756-757 (2009) (error to admit interrogating police officer’s notes of witness’s statements to police in part because admission created risk that jurors might substitute written notes for collective memory of witness’s trial testimony).
Third, the postbreak portions of the written statement, while to some extent cumulative of what the defendant had already said before the break, were far from entirely so. Moreover, some of the differences might well have increased the likelihood that the jury would view the defendant as a liar, a man who would change his story in order to avoid responsibility for his crimes. Thus, the defendant’s postbreak comments about not smoking marijuana on the night of the incident, not “do[ingj” cocaine, and only feeling “tired” (not intoxicated) from drinking five to six ounces of rum contradicted the defendant’s own trial testimony, and also conflicted directly with information he had provided to Dr. Joss, one of the two expert witnesses on whom the defendant relied at trial to explain his PTSD and its effect on him.15 And the defendant’s explicit, categorical statement, made only during the postbreak period, that he “never [323]*323had a knife in my hand the whole time” reemphasized the glaring conflict between the defendant’s version of events and what the physical evidence and other witnesses’ testimony showed — as the defendant essentially admitted at trial, when he stated he must have used a knife and slashed or stabbed the victims. Finally, the portion of the written statement that described how the defendant declined the offer to speak with his appointed lawyer, and instead chose to continue speaking to the police, could be interpreted by the jury to support a view of the defendant not only as a deliberative prevaricator — a quality suggested by the addition of his signatures to the “statement” — but as one who was also self-confident enough to talk to the police, and construct his story, on his own.
To be sure, the improperly admitted evidence at issue did not include a confession or even an inculpatory admission. Contrast Mavredakis, 430 Mass, at 853 (while attorney was waiting in police station, defendant changed from denying to admitting his involvement in shooting); McKenna, 355 Mass, at 318-320 (after defendant’s attorney had contacted police, defendant admitted participation in crime). However, the defendant’s proffered theory of defense focused almost entirely on his mental and emotional condition at the time of the critical events. In that context, the improper evidence had a real potential to weaken or even undermine the defendant’s efforts to present himself as a mentally and emotionally impaired man suffering from PTSD who, at the relevant time, overreacted to a perceived threat to his safety arising from the conduct of Linda (as well as the other two victims), dissociated from what was going on, and was unable to think or act rationally about how to extricate himself from the danger he perceived.
Turning to additional factors listed in our cases as relevant to the harmless error analysis, see Commonwealth v. Dagraca, 447 Mass, at 553; Commonwealth v. Mahdi, 388 Mass, at 696-697, we think it clear that the defendant’s complete, signed statement was significant to the prosecution. It was the prosecution that introduced the statement, through Marks. The prosecutor called Marks as her final witness, and his reading of the entire statement, followed by the admission of the written document as an exhibit, were the capstones of the Commonwealth’s case-in-[324]*324chief. The prosecutor’s cross-examination of the defendant thereafter focused repeatedly on the statement, including the defendant’s act of signing it, and she featured the statement as the first topic discussed in her closing argument. As the Commonwealth stated during oral argument before this court, the defendant’s full, signed statement was “definitely an important part of the Commonwealth’s case.” Finally, on the “weight or quantum of evidence of guilt,” Commonwealth v. Dagraca, supra, there was indeed a great deal of evidence that the defendant killed Linda and wounded the other two victims. Given the premise of the defense, however, what is critical is not the quantum of this evidence, but rather the evidence pertaining to the defendant’s mental state on the night of March 28 and into the morning of March 29, and concerning what happened between the defendant and Linda while the two were in her bedroom during this time. Little was presented on either topic. As the trial judge remarked to the attorneys, “We just don’t know what happened,” and, “Here we don’t know what the motive is.” The principal source of evidence bearing on the defendant’s mental state was the defendant’s expert witnesses and the defendant himself. Even assuming the jury’s disbelief of these witnesses, such disbelief would not create affirmative conflicting evidence. Beyond these witnesses, there was evidence that Colaban had described the defendant as without expression when he came out of Linda’s room, and evidence from witnesses who interacted with the defendant at the temporary employment agency that the defendant was acting strangely. Considering all these factors, we cannot say with assurance that the improperly admitted evidence of the defendant’s full and signed statement “might [not] have had an effect on the jury or contributed to the verdicts,” id., and that it was therefore harmless beyond a reasonable doubt.16
(ii) Convictions of assault and battery by means of a danger[325]*325ous weapon. The defendant’s convictions of two counts of assault and battery by means of a dangerous weapon stand on different ground. As discussed, the “premise of the defense” at trial, Commonwealth v. Mahdi, 388 Mass, at 696, was that the defendant’s alleged PTSD, a mental impairment, rendered him incapable of the malice necessary for murder, and we have concluded that the admission of the entire signed statement was not harmless because it could be viewed as impairing or undermining that defense. While mental impairment is relevant to the murder conviction, which requires proof of a specific intent, see, e.g., Commonwealth v. LaCava, 438 Mass. 708, 717-718 (2003), it is not relevant to these convictions. Assault and battery by means of a dangerous weapon is a general intent crime and, as such, obligates the Commonwealth to prove beyond a reasonable doubt that the defendant had a general intent to do the act causing the battery, but not that he had a specific intent to injure the victim. Commonwealth v. Appleby, 380 Mass. 296, 307 (1980). See Commonwealth v. Ford, 424 Mass. 709, 711 (1997). We do not consider mental impairment (short of a lack of criminal responsibility, which is not claimed here) relevant to the jury’s determination whether the defendant was able to form the requisite general intent. See Commonwealth v. Fano, 400 [326]*326Mass. 296, 305 n.14, 308 n.17 (1987), citing Commonwealth v. Grey, 399 Mass. 469, 474 (1987) (jury permitted to decide if mental condition “rendered the defendant unable to form the specific intent necessary for the crime of murder, but that finding would not exonerate the defendant from guilt for a crime requiring only general intent”). The defendant has not suggested on appeal that as a result either of his PTSD or intoxication, he was incapable of forming the requisite general intent. While he may not have intended the consequences of touching Colaban and AlexSandra, or while he may have felt threatened in some manner before he struck, there is no suggestion in the evidence that the defendant was not aware of any relevant circumstance or that he did not intend the touching. See Commonwealth v. Ford, supra at 711-712; Commonwealth v. Appleby, supra.
Moreover, the primary focus of the entire statement was on the defendant’s actions relative to Linda; his interactions with AlexSandra and Colaban are referenced relatively briefly, and primarily in the portion of the statement that the defendant gave before 10 a.m. — the substance of which was admissible.17 Indeed, the only postbreak reference in the statement to either Colaban or AlexSandra directly repeats something the defendant had stated prebreak, namely, that he knocked the knife out of Colaban’s hand. (There is no postbreak mention of AlexSandra.) See Commonwealth v. Perez, 411 Mass. 249, 260 (1991). Given the statement’s limited references to these victims, we are satisfied that the impact of the defendant’s signature on the pages of the statement was equally minimal. Furthermore, independent of the statement, the evidence that the defendant cut or slashed AlexSandra and Colaban was overwhelming. See id. at 261. In light of all the circumstances, we are certain that these two convictions were “surely unattributable to the [Mavredakis] error,” Commonwealth v. Vasquez, 456 Mass, at 361, quoting Sullivan [327]*327v. Louisiana, 508 U.S. 275, 279 (1993), and that, as to those convictions, the erroneous admission of the defendant’s complete, signed statement was harmless beyond a reasonable doubt.18
4. Issues that may arise at retrial, a. Voluntariness of defendant’s statement. In addition to the Mavredakis errors, the defendant claims that the entirety of his statement to the police should have been suppressed, because the Commonwealth could not prove the voluntariness of the statement beyond a reasonable doubt.19 See Commonwealth v. Auclair, 444 Mass. 348, 353 (2005). In particular, he contends that at the time of the police interrogation, he suffered from mental illness and humiliation caused by the fact that his clothes had been taken from him and he was covered only by a blanket; he also contends that “misrepresentation [of facts concerning Linda’s condition], intoxication, and mental illness” worked to render his statements involuntary.20 After an evidentiary hearing, the motion judge rejected the claim, concluding:
“[I]n the totality of the circumstances, the defendant’s statements were voluntary as the defendant’s will was not ‘[ojverbome to the extent that his statement was not the result of a free and voluntary act.’ Commonwealth v. Selby, 420 Mass. 656, 662-663 (1995). In the totality of the circumstances surrounding the questioning of the defendant, the police did not make any promises or other inducements. The defendant did not appear to the police to be tired or under the influence of drugs or alcohol, nor did the defendant appear to be emotionally unstable. The defendant was read his complete Miranda rights twice — [328]*328once during booking and again in the interview room before questioning began. Furthermore, the defendant indicated that he understood the Miranda rights by the physical voluntary act of signing the Miranda card indicating that he understood his rights.”21
In reviewing a decision of a motion judge, we accept his findings of fact absent clear error, “and a finding of voluntary waiver is given substantial deference.” Id. The motion judge was entitled to accept the testimony of the police about the defendant’s appearance and level of sobriety, see Commonwealth v. Anderson, 445 Mass. 195, 204 (2005), citing Commonwealth v. Dunn, 407 Mass. 798, 803-805 (1990), and to give weight to the repeated issuance of Miranda warnings. See Commonwealth v. Auclair, supra at 355. With respect to the claim that the defendant’s level of emotional upset was too great to permit a finding that his Miranda waiver and statements were voluntary, “emotional upset alone does not render a waiver of Miranda rights or the voluntariness of the statement itself invalid where there is no evidence that the defendant was acting irrationally [during the interrogation].” Id. See Commonwealth v. LeBlanc, 433 Mass. 549, 555 [329]*329(2001). There was no error in the denial of the defendant’s motion to suppress on voluntariness grounds.22,23
b. Admission of autopsy photographs. The defendant asserts error in the admission of certain autopsy photographs, claiming they were more prejudicial than they were probative. See Commonwealth v. Richmond, 371 Mass. 563, 565-566 (1976). The photographs in question showed the results of surgery, as well as bruising and swelling from “coagulopathy,” a condition caused when the units of blood the victim received did not clot. While we have said that unduly gruesome autopsy photographs present “special problems,” Commonwealth v. Bastarache, 382 Mass. 86, 106 (1980), a trial judge has discretion to admit them in appropriate cases. Despite showing some surgical alterations, the trial judge could properly conclude that what the photographs showed was relevant to the Commonwealth’s theory that the defendant acted with extreme atrocity or cruelty.24 See Commonwealth v. Anderson, 445 Mass, at 209; Commonwealth v. Keohane, 444 Mass. 563, 573 (2005).
[330]*330c. Admission of 911 call. The defendant also claims error in the admission over objection of a tape recording of the 911 call initiated by six year old Tatiana in the apartment’s kitchen, who was neither a stabbing victim nor a witness at trial. In the recording, Tatiana screamed, “He’s killing us,” and ten year old AlexSandra told the police that the knife “went right through me.” The trial judge expressed reservations about admitting the evidence, because “it’s very emotional” and “doesn’t tell [us] much,” but allowed the recorded call to be played to the jury, finding that it went to the Commonwealth’s theory of extreme atrocity and cruelty. While hearing the two children’s panicked 911 call to the police may be relevant to Linda’s own emotional suffering, and therefore also relevant to the issue of extreme atrocity or cruelty, cf. Commonwealth v. Murphy, 426 Mass. 395, 402 (1998) (defendant killed victim, his wife, in presence of their two year old son); Commonwealth v. Barros, 425 Mass. 572, 581 (1997) (defendant killed victim in presence of victim’s wife and friend), it is not clear from the record whether Linda, although still alive, was able to hear the call. Absent any such evidence, the recording of the 911 call may well be more prejudicial than probative, and appropriately excluded.25,26
[331]*3315. Conclusion. The judgments of conviction of assault and battery by means of a dangerous weapon are affirmed. The judgment of conviction of murder in the first degree is reversed, and the verdict is set aside. The case is remanded for a new trial on the murder indictment, and further proceedings consistent with this opinion.
So ordered.