Liacos, C.J.
The defendant, Wilbert Scott, was convicted by a jury on October 8, 1987, of murder in the first degree. He appeals from his conviction. He asserts various claims of error, each of which we discuss below. We affirm the conviction.1
The evidence before the jury was as follows. The victim, a nineteen year old woman, left her job as a nurse’s aide at the Bolton Manor Nursing Home in Marlborough at approximately 9 p.m. on Monday, July 28, 1986. She walked toward her boy friend’s apartment, about one and one-third miles away. Four motorists testified that they saw a young woman wearing a white uniform, walking along Bolton and Lincoln Streets in Marlborough. The victim did not arrive at her boy friend’s apartment.
Three days later, on the afternoon of Thursday, July 31, 1986, the victim’s body was found in a wooded area near the corner of Lincoln and Cashman Streets in Marlborough. She was lying on her back, wearing only her white uniform skirt. Her bra was open in the front, exposing her breasts. Her shoes, socks, and underwear were found behind a rock nearby. A T-shirt and an oxford shirt, both of which belonged to the victim, were tied together behind her head and used as a gag to cover her mouth. The victim’s face was abraded and bruised. From the injuries, it was determined that she was struck in the face at least three times with an object consistent with being either a closed fist or an open hand. The blows to the face rendered the victim unconscious or semi-conscious. The reduced level of consciousness made it [813]*813impossible for the victim either to untie the gag or to free her tongue, which was pushed back by the gag. The victim died from a combination of head injuries and asphyxia by the gag. There was no evidence of sperm or seminal fluid; there was no evidence of injury to her genital organs.
The defendant lived in an apartment across the hall from the victim’s boy friend. He was arrested on August 4, 1986. After he was arrested, the police searched the defendant’s apartment pursuant to a search warrant and seized several items of clothing and bedding belonging to the defendant.
At trial, the Commonwealth introduced the testimony of Special Agent Andrew Gary Podolak of the Federal Bureau of Investigation. Podolak testified that he performed an examination of two Negroid hairs found on the victim’s body. One Negroid hair exhibited the same microscopic characteristics as the defendant’s hair. This hair was found embedded in the victim’s sock. Another Negroid hair, which did not match the hair characteristics of the defendant, was found on the victim’s thigh. In addition, six Caucasian hairs, which matched the microscopic characteristics of the victim’s hair, were found on clothing seized at the defendant’s apartment. One of these hairs was found on the inside of a pair of white shorts owned by the defendant.
A witness testified that she saw the defendant wearing shorts that were a “light color” on the night the victim was killed. The other hairs belonging to the victim were found on the defendant’s underpants, socks, and dungarees.2
After his arrest, and in his testimony at trial, the defendant stated that on July 28 he got home from work at 6 p.m. and went to bed because he was not feeling well. However, John Reilly, who lived a short distance from the empty wooded lot where the victim was found, testified that he saw [814]*814the defendant walking by his house a few minutes before 9 P.M.
On Tuesday, August 5, 1986, the defendant, while being held in a cell at the Marlborough District Court, spoke with another inmate. The inmate, who was aware that the defendant was arrested for murdering a young woman, told the defendant that he hoped “it was worth it. You ain’t going to get nothing for a long time.” The defendant responded that “[s]he had firm breasts.” The defendant also told the inmate that he had seen the victim in the halls of his apartment building and that she was “very pretty.”
A few days after the defendant’s arrest, a neighbor entered the defendant’s apartment and saw several pornographic magazines on the floor. He noticed that the top magazine had an article about a serial killer, and he proceeded to read it. He testified at trial that the article was about a serial killer who had killed several young women by stuffing pieces of cloth into their mouths, gagging and eventually strangling his victims.
Finally, the Commonwealth introduced evidence that three young women were harassed by the defendant a few days before the victim’s death. Karen Sullivan testified that on July 23, 1986, the defendant followed her from the store where she worked to her friend’s apartment. On July 26, the defendant returned to the apartment house. Fifteen year old Kathy Boivin answered the door. After the defendant asked if she was alone, Boivin closed the door. Later that afternoon, as Boivin returned home, she saw the defendant across the street. He called her “beautiful,” asked her to come over, and told her that he would not hurt her. Boivin continued walking.
On the evening of July 26, the defendant went to a bar in Marlborough and played pool with Lisa Sullivan, a pregnant twenty-four year old woman. After the game of pool, the defendant put his hand on Sullivan’s wrist and asked her to. go home with him. She refused. A few minutes later she left the bar.' The defendant followed Sullivan. After Sullivan got into her automobile, the defendant jumped on the hood of her au[815]*815tomobile and banged his fists against the windshield. Sullivan drove out of the parking lot, and the defendant fell off the automobile. Sullivan stopped for a red traffic light at a nearby intersection. She observed the defendant running towards her, and she drove away.
1. Possible exculpatory witness. Almost one year before the trial, the Commonwealth informed the defendant that another woman was assaulted on July 28, 1986, between midnight and 1 a.m., on Lincoln Street in Marlborough, a short distance from where the body of the victim in this case was found. The assault was reported to the Marlborough police department by a person other than the victim. The Marlborough police interviewed the woman. She confirmed that she was assaulted by a white male, five feet six inches or five feet seven inches in height, 150-170 pounds, dark hair, in his early thirties. On January 15, 1987, the defendant filed a motion for access to the victim, and, on February 3, 1987, a hearing was held. At the hearing, the prosecutor and the victim’s own attorney argued that the potential witness was suffering from severe psychological trauma as the result of the assault and that she did not want to speak to anyone about the incident.3 On February 11, 1987, the judge denied the defendant’s motion. The judge did not give reasons for the denial of the motion.
The defendant argues that he has a right of investigative access to the victim of this other crime under the Fifth and Fourteenth Amendments to the United States Constitution and under art. 12 of the Massachusetts Declaration of Rights. We must determine whether the victim of the second crime had information which was both material and exculpatory.
It is well established that a defendant should be allowed to “introduce evidence that another person recently committed a similar crime by similar methods, since such evidence tends to show that someone other than the accused committed the [816]*816particular crime.” Commonwealth v. Jewett, 392 Mass. 558, 562 (1984). We have stated previously that evidence involving crimes of a similar nature by a person other than the defendant must be admitted when “the acts of such other person are so closely connected in point of time and method of operation as to cast doubt upon the identification of [the] defendant as the person who committed the crime.” Commonwealth v. Keizer, 377 Mass. 264, 267 (1979), quoting State v. Bock, 229 Minn. 449, 458 (1949). See Commonwealth v. Murphy, 282 Mass. 593 (1933). In determining whether to admit evidence of crimes committed by individuals other than the defendant, the usual considerations of relevancy apply. Commonwealth v. Jewett, supra. It is for the trial judge to determine whether to admit or reject evidence of crimes committed by other individuals. Commonwealth v. Lawrence, 404 Mass. 378, 387-388 (1989). Commonwealth v. Harris, 395 Mass. 296, 300 (1985). We will not disturb the trial judge’s decision unless justice requires a different result. Commonwealth v. Keizer, supra. Commonwealth v. Murphy, supra at 598.
We are not convinced that justice requires us to disregard the judge’s ruling on the materiality of the evidence. It is true that the attacks occurred a short distance from, and within three or four hours of, each other. The defendant, however, did not present any evidence during the motion hearing which established that the method of operation of both crimes was similar. See Commonwealth v. Brown, 27 Mass. App. Ct. 72, 76 (1989) (“[a]part from considerations of proximity in time and location, the instant and the similar crime must share singular features or present striking resemblances of method”). Since we do not know the method of attack used by the second assailant, nor the factual characteristics of the second assault, we cannot say that justice requires us to disregard the judge’s ruling that the victim did not have material information.
The defendant could have had access to the alleged exculpatory and material information by asking for a copy of the [817]*817police report.4 Since the victim was unwilling to discuss the case with anyone, it is uncertain whether the defendant would have learned any relevant information, even if the judge had granted his motion. The victim could have declined to speak with the defendant’s counsel. See Commonwealth v. St. Pierre, 377 Mass. 650, 658 (1979). The police report, however, may have contained valuable exculpatory information for the defendant. If the defendant had made a specific request for the police report, and the report in fact contained exculpatory and material information, the prosecutor would have been constitutionally required to provide the report to the defendant. See Commonwealth v. Gallarelli, 399 Mass. 17 (1987); Commonwealth v. Ellison, 376 Mass. 1 (1978). The defendant had within his reach the information which, he now argues, was vital to his defense. He failed to pursue the remedies available to him. Thus, on this record, we conclude that the trial judge did not err in denying the defendant investigatory access to the victim of the second assault.5
2. The defendant’s prior bad acts. Defense counsel objected to the introduction in evidence of the defendant’s harassment of three young women a few days before the victim [818]*818was killed. It is well established that the Commonwealth may not introduce evidence of prior bad acts by the defendant to prove bad character or a propensity to commit crimes. See Commonwealth v. Trapp, 396 Mass. 202, 206 (1985); Commonwealth v. Stone, 321 Mass. 471, 473 (1947). The Commonwealth, however, may introduce such evidence to prove intent, motive, identity, pattern of operation, or common scheme. See Commonwealth v. Helfant, 398 Mass. 214, 224, 225 (1986), and cases cited.
The Commonwealth filed a motion in limine to admit the evidence of the defendant’s prior bad acts, arguing that the prior misconduct was evidence of the defendant’s sexual frustrations. The trial judge granted the motion, ruling that the prior bad acts were relevant to the Commonwealth’s theory of motive or intent.
The defendant argues that the incidents of harassment of the three young women were admitted to show propensity for criminal behavior and not to establish plan, motive, or intent. The defendant claims that the incidents of harassment had a low probative value since they were not sufficiently similar to the crime for which he was indicted. The defendant concludes that the admission in evidence of his prior misconduct was unduly prejudicial. See Commonwealth v. Welcome, 348 Mass. 68 (1964); Commonwealth v. Key, 21 Mass. App. Ct. 293 (1985). The Commonwealth argues that the defendant’s overtures to the three young women were relevant to show the defendant’s sexual frustration and thus his plan, motive, and intent to procure a sexual encounter at the time of the murder. We agree.
In Commonwealth v. Bradshaw, 385 Mass. 244 (1982), the prosecution’s theory was that the defendant killed the victim because of frustration over a lack of money. The victim was demanding that a third party pay him a sum of money which the third party had already given to the defendant. In support of its theory, the Commonwealth portrayed the defendant’s activities during the day of the mur[819]*819der as a desperate search for money.6 We found no error in the admission of the evidence, since it was relevant to show intent or motive.7 In Commonwealth v. Rancourt, 399 Mass. 269 (1987), the defendant was charged with rape. In that case, we stated that the “defendant [’s] attempt [ ] forcibly to enter an automobile in which two women were riding shortly before he entered the victim’s automobile ... is relevant on the critical issues of intent, motive, and consent.” Id. at 275-276.8
It is for the trial judge to determine whether the prejudicial effect of evidence outweighs its probative value. The decision of the judge will be accepted on review unless the judge committed palpable error. See Commonwealth v. Young, 382 Mass. 448, 462-463 (1981). Commonwealth v. Hoffer, 375 Mass. 369 (1978). There was no such error in this case. The incident involving Lisa Sullivan, where the defendant followed her out of the bar, leaped onto the hood of her automobile, banged his fists against the windshield, fell off the automobile, and then ran after Sullivan as she drove away is probative evidence of the defendant’s plan, motive, and intent to assault the victim in the instant case. The incidents involving the harassment of Karen Sullivan and Kathy Boivin are more problematic, since they did not involve physical violence or threats. The two incidents, however, when combined with the more serious harassment of Lisa Sullivan, were relevant evidence in showing that the defendant may [820]*820have been sexually frustrated. See Commonwealth v. Rancourt, supra; Commonwealth v. Bradshaw, supra at 269-270.9
3. Evidence of rape and felony-murder. At the close of the Commonwealth’s case and again at the close of the defendant’s case, the defendant moved for a required finding of not guilty on so much of the indictment as alleged murder in the first degree. The judge denied both motions. The judge, during the charge, instructed the jury that they could find the defendant guilty of murder in the first degree if they found premeditation or if they found that the defendant committed a felony punishable by life imprisonment. See G. L. c. 265, § 1 (1988 ed.). The judge explained to the jury that, in order to find the defendant guilty of murder in the first degree on the theory of felony-murder, they must find that the Commonwealth proved beyond a reasonable doubt that the defendant committed aggravated rape or attempted aggravated [821]*821rape. See G. L. c. 265, § 22 (a) (1988 ed.). The jury found the defendant guilty of murder in the first degree on the theory of felony-murder. The defendant argues that the judge erred in denying his motions for a required finding.
The rule of felony-murder substitutes the intent to commit the underlying felony for the malice aforethought required for murder. Commonwealth v. Troy, 405 Mass. 253, 262 (1989). Commonwealth v. Moran, 387 Mass. 644, 649 (1982). In order to benefit from the principle of constructive malice embedded in the felony-murder rule, the Commonwealth must prove the malice element of the underlying felony beyond a reasonable doubt. Commonwealth v. Chub-buck, 384 Mass. 746, 756 (1981). Commonwealth v. Watkins, 375 Mass. 472, 487 (1978). The underlying felony must be inherently dangerous to human life, and it must be committed in circumstances which demonstrate the defendant’s conscious disregard of the risk to human life. Commonwealth v. Moran, supra. Commonwealth v. Matchett, 386 Mass. 492 (1982). The commission of attempted aggravated rape satisfies the malice requirement of felony-murder. See Commonwealth v. Troy, supra.10
We must determine whether “the evidence was insufficient to persuade a rational trier of fact of each of the elements of the crime charged beyond a reasonable doubt.” Commonwealth v. Sherry, 386 Mass. 682, 687 (1982). In making such a determination, we consider the evidence in the light most favorable to the Commonwealth. Commonwealth v. Wilborne, 382 Mass. 241, 244 (1981). See Commonwealth v. Latimore, 378 Mass. 671, 676-677 (1979).
There is no evidence that the defendant penetrated the victim. See Commonwealth v. Gallant, 373 Mass. 577, 578 (1977). We believe, however, that there was sufficient evidence for a rational jury to find that the defendant attempted to rape the victim. In order for acts of preparation to qualify [822]*822as an attempt, they must “come[ ] very near to the accomplishment of the [criminal] act.” Commonwealth v. Peaslee, 177 Mass. 267; 272 (1901). The victim in the instant case was found on her back, wearing only her skirt, with her underpants removed, her shirt ripped.off, her bra unfastened, and her breasts exposed. The underpants, along with the victim’s socks and shoes, were found nearby behind a rock. One of the victim’s hairs was found inside a pair of shorts that the defendant was seen wearing on the night on which the victim was killed. The hair was found underneath the side pocket next to the zipper. This was sufficient evidence for a rational jury to infer that the defendant attempted, but ultimately failed, to penetrate the victim.
Attempted rape, by itself, however, cannot be the underlying felony for murder in the first degree.11 There must be evidence of aggravation. Under the statute, a rape becomes aggravated if it is “committed with acts resulting in serious bodily injury ... or is committed during the commission or attempted commission of [an assault and battery with a dangerous weapon].” G. L. c. 265, § 22 (a).
A gag is not a per se dangerous weapon. It is for the jury to determine whether an object, which is not per se dangerous, was used as a dangerous weapon by the defendant, taking into account the purposes for which the object is intended and the manner in which it is used. Commonwealth v. Appleby, 380 Mass. 296, 307 (1980). Commonwealth v. Farrell, 322 Mass. 606, 615 (1948). Commonwealth v. Marrero, 19 Mass. App. Ct. 921, 922-923 (1984). The defendant argues that it was not foreseeable that the gag would cause death by asphyxia, and therefore that the gag was not used as a dangerous weapon. We disagree. We hold that there was [823]*823sufficient evidence for the jury to find that the gag, as used by the defendant, was a dangerous weapon.12
4. Impeachment of a Commonwealth witness. James Woods testified that on July 28, 1986, the night on which the victim was killed, he was in Bert’s Lounge, a bar down the street from where the defendant lived. Woods, who was the only black man at Bert’s at the time, testified that he saw another black man walk into the bar. He described the man as five feet eight inches or five feet nine inches in height, with dark complexion. Woods, however, added that he did not look at the individual’s face. Woods stated that a police officer later showed him an array of pictures, but that he was unable to choose the individual who entered Bert’s that evening from the picture array. Woods was also unable to make an in-court identification of the defendant.
Marlborough police Officer Lawrence Moffa testified that on August 8, 1986, he showed Woods a photographic array and asked him whether he recognized the black man whom Woods saw at the bar. According to Moffa, Woods picked the defendant’s photograph. At the request of defense counsel, the judge instructed the jury that Moffa’s testimony had no probative value and was being offered by the Commonwealth to impeach Woods’s testimony.13 The defendant argues that the purported pretrial identification should not be admissible to impeach a witness who denies having identified the defendant in a pretrial identification procedure as the person whom the witness saw commit, not the actual crime, [824]*824but a collateral act not related in any way to the commission of'the crime. We disagree.
A party may impeach the credibility of his own witness by proving that the witness made prior inconsistent statements. G. L. c. 233, § 23 (1988 ed.).14 Testimony that the witness made a pretrial identification, when the witness denies in court to having made the identification, is not admissible for its probative worth. Commonwealth v. Daye, 393 Mass. 55, 61 (1984). “[A] police officer’s attribution to a witness of a positive identification denied by the witness at trial is not admissible to prove the identification.” Id. A party, however, may impeach his own witness even when the witness denies having made the pretrial identification. Commonwealth v. Swenson, 368 Mass. 268 (1975). See also Commonwealth v. Jones, 407 Mass. 168, 169 (1990).
As the judge’s instructions made clear, Moffa’s testimony was offered not to prove that the defendant was in the bar on the evening of July 28, 1986, but to impeach Woods’s denial of having identified the defendant from the photographic array. The judge did not err in admitting Moffa’s testimony.
The defendant asks us to limit Commonwealth v. Swenson, supra, to those cases where the purported pretrial identification of the defendant occurred while the witness supposedly observed the defendant commit the actual crime. The defendant argues that the rule announced in Commonwealth v. Swenson, supra, should not apply in situations when the witness denies at trial having identified the defendant as the person who engaged in an act which, by itself, was innocent but which fits into the Commonwealth’s theory of circumstantial evidence. The defendant argues that, in the absence of any other evidence that the defendant was in the bar that [825]*825evening, there was no purpose in admitting Moffa’s testimony. The defendant appears to confuse the difference between substantive and impeachment evidence. The fact that there was no other evidence placing the defendant at the bar on July 28, 1986, is not important since, as explained above, the evidence was not admitted to identify whom Woods saw entering the bar that evening. Instead, Moffa’s testimony was admitted for the limited, and entirely appropriate, purpose of impeaching Woods’s denial of having made a pretrial identification of the defendant.
5. Failure to suppress identification. John Reilly, a resident of Marlborough who lives a short distance from the wooded lot where the victim’s body was found, identified the defendant from several photographic arrays as the man he saw walking down his street a few minutes before 9 p.m. on July 28, 1986. Sergeant Jusseaume of the Marlborough police department showed Reilly a group of four different photographic arrays over a period of several days. Jusseaume testified at trial that Reilly did not pick out any of the photographs in the first two arrays. Jusseaume also testified that the defendant’s photograph was not included in the first two arrays. During the presentation of the third and fourth arrays, Reilly picked out two photographs, one of which was the defendant’s. The photograph of the defendant which was shown to Reilly by Jusseaume was overexposed. On August 4, 1986, the defendant was arrested and a new photograph of him was taken. That evening, Detective Pitard of the Marlborough police department brought an array of photographs to Reilly’s house. Included in the array was the new photograph of the defendant. Reilly identified the defendant’s photograph. The defendant filed a motion to suppress the identification. The motion was denied.
The defendant argues that the repeated showings of the arrays to Reilly, coupled with the inclusion in the last array of a new, and apparently better, photograph of the defendant, was unnecessarily suggestive and thus violated his due process rights under the Fifth and Fourteenth Amendments, and under art. 12.
[826]*826The defendant has the burden by a preponderance of the evidence to show that the challenged procedure was “ ‘so unnecessarily suggestive and conducive to irreparable mistaken identification’ as to deny the defendant due process of law.” Commonwealth v. Venios, 378 Mass. 24, 27 (1979), quoting Stovall v. Denno, 388 U.S. 293, 301-302 (1967). In other words, “[p]hotographic identification procedures are constitutionally invalid if the procedures were ‘so impermissibly suggestive as to give rise to a very substantial likelihood of irreparable misidentification.’ ” Commonwealth v. Thornley, 406 Mass. 96, 98 (1989), quoting Simmons v. United States, 390 U.S. 377, 384 (1968). See Commonwealth v. Botelho, 369 Mass. 860, 867-868 (1976).
While the danger of misidentification is increased if the photograph of the same individual is included in different arrays, simple repetition is not sufficient, by itself, to make the identification procedures unnecessarily suggestive.15 See Commonwealth v. Paszko, 391 Mass. 164, 169-170 (1984). The fact that a new, better photograph of the defendant was included in the last array from which Reilly positively identified the defendant is also not unnecessarily suggestive. See Commonwealth v. Paszko, supra at 171 (no unconstitutional suggestiveness when photographs are substantially different and witness made identification from more recent photograph). Since the identification procedures were not unnecessarily suggestive, the judge did not commit error in denying the defendant’s motion to suppress the identification.
6. Bifurcation. Finally, the defendant argues that his two possible defenses, lack of criminal responsibility and identity, were inconsistent with each other. The defendant argues that, in pursuing a lack of criminal responsibility defense, it is in a defendant’s interest to raise any past history of mental problems. In an identity defense, on the other hand, it is in a defendant’s best interest to exclude all evidence of mental problems.
[827]*827A defendant does not have a constitutional right to a bifurcated trial as to the issues of criminal conduct and criminal responsibility. Commonwealth v. Bumpus, 362 Mass. 672 (1972), judgment vacated and remanded on other grounds, 411 U.S. 945 (1973), afFd on rehearing, 365 Mass. 66 (1974), petition for habeas corpus sub nom. Bumpus v. Gunter, 452 F. Supp. 1060 (D. Mass. 1978). See Commonwealth v. Haas, 373 Mass. 545, 562 (1977), S.C., 398 Mass. 806 (1986). The decision to grant a bifurcated trial is within the sound discretion of the judge. Commonwealth v. Siegfriedt, 402 Mass. 424, 431 (1988). In denying the motion for a bifurcated trial, the judge expressed concern that there would be an overlap between the evidence needed to establish the defendant’s criminal responsibility and the evidence relevant to the voluntariness of the defendant’s statements to the police, even if the defendant did not contest voluntariness. The judge also noted that evidence of a lack of criminal responsibility was related to the mens rea component of the crime. We find no abuse of discretion on the part of the judge.
Judgment affirmed.