GANTS, J.

On October 10, 2005, Sylvia Mazur discovered the body of her eighty-three year old mother, Rose Ann Martowski (victim), on the sofa of her mother's home in Ware. The victim's skull had been fractured so severely that the entire right side of her skull had collapsed, leaving her brain exposed and her face bloodied. The home had been ransacked, and the victim's jewelry and cash were gone. A fire had been set on the bed in the victim's bedroom, but it had extinguished itself. A jury in the Superior Court convicted the defendant of murder in the first degree on theories of deliberate premeditation, extreme atrocity or cruelty, and felony-murder, and of armed burglary and arson.1 On appeal, the defendant argues that he should be granted a new trial because the trial judge erred by (1) improperly barring third-party culprit evidence; (2) admitting in evidence the medical examiner's opinion as to the type of weapons that were consistent with the victim's injuries; and (3) denying four of the defendant's challenges for cause during jury selection. We conclude that the judge did not err in any of these rulings, and affirm the defendant's convictions. After a complete review of the record, we also conclude that there is no basis to exercise our power under G. L. c. 278, § 33E, to reduce his murder conviction to a lesser degree of guilt or to order a new trial.

Background. Because the defendant does not challenge the sufficiency of the evidence, we provide only a summary of the evidence, viewed in the light most favorable to the prosecution, reserving certain details for our analysis of the issues raised on appeal.

Frank Gurka hired the defendant between September 7 and September 11, 2005, to help him load and sell antiques and collectibles at the Brimfield Fair. On September 17, Gurka and his wife returned from another antiques fair at approximately 11 P.M. and went to bed. The next morning, Gurka discovered that the bathroom window and screen in his home had been opened, approximately $150 in cash had been removed from a money pouch in the parlor, and a collectible bottle commemorating the flight of Apollo 15 was missing. On July 21, 2006, the defendant gave the Apollo 15 collectible bottle as a birthday present to his friend, Joseph Brown.

At approximately 5 P.M. on October 9, 2005, the victim's next door neighbor, ninety-four year old Sophie Cloutier, saw a man stare for about ten minutes at the rear of the victim's house.2 That night, she saw a "smoky" light in the victim's home, which was unusual because she had never seen lights that late at night in the victim's home. Later that day, after the victim's body had been discovered and the police had secured the crime scene, the police observed that the kitchen window above the sink in the victim's home was open, there was a footwear impression at the base of the kitchen window, and an unsmoked Camel "wide filter" cigarette was lodged between the screen and window. The defendant smoked Camel wide cigarettes. The cigarette was sent for deoxyribonucleic acid (DNA) testing, which revealed a partial male DNA profile from a single source that matched the defendant's DNA profile. The probability of another randomly selected individual besides the defendant having the same DNA profile was approximately one in 6.242 billion of the Caucasian population, one in 2.737 billion of the African-American population, and one in 2.492 billion of the Hispanic population. When interviewed by the police, the defendant said that he did not know where the victim's residence was located, and that there was no reason why his DNA might be inside that house.

The victim had no checking account and paid her bills with money she kept in her handbag. Approximately three weeks before her death, the victim had an estimated $3,000 in cash, much of it in $100 and $50 denominations, and was scheduled to receive her monthly Social Security check at the beginning of October. The handbag with the cash was gone when her body was discovered.

The defendant, who was unemployed at the time of the victim's death but a frequent user of cocaine, marijuana, and other drugs, had a "good-size wad of money" on the morning of October 11, 2005, and used a $100 bill to purchase video game products. About a week before Halloween in 2005, the defendant gave a bracelet to a friend, and showed her a green metal box containing other jewelry that the friend described as "[w]hat an older woman would wear ... something my grandmother would have." Two days later, he told her that he had won about $3,000 on a "scratch ticket" and carried a wad of twenty dollar bills. Later in the fall of 2005 he purchased one-quarter pound of "the next step up type of" marijuana, costing approximately $900, which he paid with $50 and $100 bills; he had been purchasing $20 or $40 bags of lesser quality marijuana in the summer and early fall of 2005. The defendant late that fall also purchased one-half ounce of cocaine for $400.

In a house of correction awaiting trial, the defendant admitted to one detainee that he had broken into a home in Ware and beat an "old lady" to death. He boasted that breaking and entering was an "art form," that he was very skilled and well prepared, that he always entered through a window, and that he always wore a hat and gloves to avoid leaving any evidence behind.3 He said that he knew the victim and she knew him, that he took some money, coins, jewelry, and an old jewelry box, and that, after "whacking" her, he gathered some papers, poured perfume over them, lit them, and left.4 He said his only mistake was in leaving the cigarette, which he had used to hold up the window screen.5

The defendant told another detainee that he had burned holes through the window screen with a cigarette to get through the window, that the woman approached him, and he got scared and hit her in the head several times with a hammer, and later threw the hammer into a lake or stream in the back of her home.6

Discussion. 1. Third-party culprit evidence. The defendant contends that the judge erred in excluding third-party culprit evidence regarding four individuals who could have committed the crimes charged, alone or together: Joseph Brown, Gregory Babb, Richard Chartier, and Kenneth Kowalski.

We declared in Commonwealth v. Silva-Santiago, 453 Mass. 782, 800-801 (2009):

The defendant claims that this evidentiary standard for the admissibility of third-party culprit evidence violates the standard established by the United States Supreme Court in Holmes v. South Carolina, 547 U.S. 319 (2006) (Holmes), under the due process clause of the Fourteenth Amendment to the United States Constitution. In Holmes, the Court set forth two "widely accepted" formulations of "rules regulating the admission of evidence proffered by criminal defendants to show that someone else committed the crime with which they are charged." Id. at 327. The two formulations provide:

Id., quoting 41 C.J.S., Homicide § 216, at 56-58 (1991).

Holmes, supra, quoting 40A Am. Jur.2d, Homicide § 286, at 136-138 (1999).7

We see nothing in either of these two "widely accepted" formulations of the evidentiary standard for the admissibility of third-party culprit evidence that is inconsistent with our standard. All consider whether the third-party culprit evidence tends to prove that someone other than the defendant committed the crime, or whether the evidence is speculative, remote, or lacks any connection with the crime charged.

The defendant, however, contends that our standard is unfair because it admits a defendant's exculpatory third-party culprit evidence only where it is of "of substantial probative value, and will not tend to prejudice or confuse," Commonwealth v. Keizer, supra, quoting Holt v. United States, 342 F.2d 163, 166 (5th Cir.1965), while a prosecutor's inculpatory evidence is admitted unless "its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, misleading the jury, being unnecessarily time consuming, or needless presentation of cumulative evidence." Mass. G. Evid. § 403 (2010), and cases cited. There is no evidentiary double standard and, consequently, no unfairness. Where evidence is otherwise admissible, "[n]ormal relevancy considerations apply in determining the admissibility of evidence that someone else committed the crime." Commonwealth v. Conkey, supra. See Commonwealth v. Jewett, 392 Mass. 558, 562 (1984). In Commonwealth v. Keizer, supra, we said that "all doubt should be resolved in favor of admissibility" of the third-party culprit evidence where "the proffered evidence is of substantial probative value, and will not tend to prejudice or confuse." Id., quoting Holt v. United States, supra. The same could be said about prior bad act evidence offered against a defendant.

Applying this standard to our independent review, we evaluate separately the defendant's claim of error as to each alleged third-party culprit. See Commonwealth v. Conkey, supra at 66-67 ("Because the issue is one of constitutional dimension, we are not bound by an abuse of discretion standard, but rather examine the issue independently"). The jury heard substantial evidence regarding Brown. They learned that Brown was the defendant's friend, that the Apollo 15 bottle stolen from the Gurka residence was retrieved from Brown's residence on September 7, 2006, and that the defendant in the summer of 2005, after asking someone at a party to help him break into a house in East Longmeadow, left the party that night with Brown. They also learned that a DNA sample was taken from Brown and that he was excluded as a source of the DNA profile found on the cigarette. The only evidence that the defendant contends the judge erred in excluding was that Brown was interviewed about the Gurka burglary, which would suggest that he was a suspect in the burglary based on his possession of the Apollo 15 collectible bottle.8 The fact that a third party was a suspect in the police investigation is not evidence that the third party committed the crime, just as the prosecutor's decision to seek an indictment against the defendant is not evidence that the defendant committed the crime. The judge did not err in excluding this evidence.

The jury heard even more evidence as to Babb. The jury learned that he lived next door to the victim's residence, in the same house as Sophie Cloutier, that he was alone with Cloutier on the evening of October 10, 2005, and that he smoked. The jury also learned that a DNA sample was taken from Babb and that he, too, was excluded as a source of the DNA profile found on the cigarette. In addition, the jury learned that shoes were taken from his residence and eliminated as the source of the footwear impression left beneath the victim's open kitchen window; that fingerprints were taken from him and did not match any of the latent fingerprints found in the victim's residence; that a hatchet in Babb's residence found near a wood pile tested negative for blood; that he was interviewed during the course of the criminal investigation; and that, when his hands were tested for the presence of blood on October 10, 2005, the test did not reveal the change in color that suggested the presence of blood.9 The defendant claims that the judge erred in refusing to let Joyce Bousquet, one of the victim's daughters, testify that the police considered Babb a suspect, that her mother had been nervous about Babb, or that she had heard that Babb had a criminal record and had been in jail.10 We conclude that the judge did not err in excluding this evidence.

As to Chartier, the jury learned only that his known DNA sample was excluded as a source of the DNA profile found on the cigarette, and that he was interviewed during the investigation. The defendant argues that the judge erred by barring him from eliciting from Sergeant Christopher Wilcox of the State police, who traveled to Georgia to interview him, that Chartier admitted to smoking Camel wide filter cigarettes, had a warrant lodged against him by the United States Army, carried a small hatchet for his work at a paper mill, had lost between $400 and $500 each month in "online gambling," and said during the interview with Sergeant Wilcox that he figured the State trooper was there because of the murder in Ware. This evidence, considered collectively, is not of probative value in suggesting Chartier's guilt. While Chartier may smoke the same type of cigarette found at the scene, the defendant's DNA, not Chartier's, was found on that particular cigarette. A small hatchet is not so unique a tool that its possession would suggest Chartier's responsibility for the victim's death. Nor would his alleged violation of the military code, or his financial problems, reasonably suggest that he was the killer. And it did not suggest consciousness of guilt that Chartier figured that the well-publicized murder of an elderly woman in Ware was the reason why a State trooper traveled to Georgia to interview him. The judge did not err in excluding this evidence.

As to Kenneth Kowalski, the defendant claims that the judge erred in barring evidence that Kowalski's girl friend was a known "crack" cocaine addict and that he walked out of his interview with Sergeant Wilcox after the trooper accused him of killing the victim to support her drug habit. A State trooper's suspicion is not probative evidence of guilt, nor, standing alone, is speculation that Kowalski committed the burglary of the victim's home because he needed money to buy drugs for his girl friend. There was no error in excluding this evidence.

In sum, we conclude that the judge carefully evaluated the probative value of the proffered third-party culprit evidence and the risk of unfair prejudice to the Commonwealth from the admission of such speculative and remote evidence, and correctly ruled that the evidence was not admissible.

2. Admission in evidence of medical examiner's opinion as to the type of weapons that were consistent with the victim's injuries. Dr. Joann Richmond, the medical examiner who conducted the autopsy of the victim, testified that the nature of the victim's wounds "tells me that the edge of the weapon that cut this piece of tissue was thick and somewhat dull; not like a scalpel, not like a knife; something that would be thicker and duller so that the edges of the tissue are scraped and not surgically cut.... It would be something more along the lines of perhaps a small axe or hatchet." Later, when asked for her opinion as to the types of weapons that would be consistent with the victim's injuries, Dr. Richmond, over objection, stated that the "type of weapon used would be something along the lines of a machete, a small hand axe, some type of meat cleaver." She later testified, also over objection, that she observed and purchased at a Home Depot store a drywall hammer, whose heaviness and sharp edge was consistent with the pattern of injuries she observed on the victim. She showed the jury the drywall hammer, which was marked for identification but not offered in evidence.

The defendant argues that the judge abused his discretion in admitting this evidence, because no weapon linked to the murder was found and the medical examiner's opinion was mere speculation. We disagree. The expert's training and experience allowed her to offer an opinion as to the type of weapon that was consistent with the type of injuries suffered by the victim. Where the prosecution offered evidence that the defendant had access to a drywall hammer in 2005 and had an axe and a ball peen hammer in his room when his parents' residence was searched on September 22, 2006, evidence that these types of tools were consistent with the injuries inflicted on the victim was relevant and not unfairly prejudicial. See Commonwealth v. James, 424 Mass. 770, 779 (1997) (possession by defendant of instrument capable of being used in commission of crime admissible without direct proof that instrument was the one used).

Nor did the judge err in allowing the expert to show the jury a drywall hammer. Dr. Richmond made clear that she had purchased the drywall hammer a couple of weeks earlier; there was no risk that the jury would mistakenly think that her drywall hammer was the murder weapon. The drywall hammer allowed her to show the jury the qualities of a weapon consistent with the type of injuries inflicted. The judge acted well within his discretion in concluding that the jury would benefit from such an illustrative example, and that the benefit exceeded the risk of unfair prejudice.

3. Denial of the defendant's challenges for cause. The defendant claims that the judge erred in denying four challenges for cause during jury selection, and that the error requires a new trial because the defendant exhausted his peremptory challenges on jurors who should have been excused for cause. A judge has broad discretion in deciding whether a prospective juror is impartial, and his decision will be reversed only for an abuse of discretion. Commonwealth v. Auguste, 414 Mass. 51, 56-57 (1992). We conclude the judge properly exercised his discretion.

We address each of the cause challenges separately. Juror no. 118, when he was a law student, served as an intern in an elder care unit of a legal services office, where he heard "some stories of elder abuse." He was sympathetic toward the elderly and, as an attorney, devotes part of his practice to helping them with matters involving Social Security and "MassHealth" applications. A member of his family had been raped. The judge questioned him as to each of these matters and the prospective juror declared that none would affect his ability to be fair in this case. The judge acted within his discretion in finding the juror honest and concluding that he would be fair and unbiased. See Commonwealth v. Leahy, 445 Mass. 481, 494 (2005) ("jurors' assertions of impartiality should be accepted by the judge unless extraordinary circumstances give some reason to question such assertions"). The fact that the juror sympathized with the elderly and that a family member has been a victim of violence does not suggest that he would not be fair in deciding whether the Commonwealth met its burden of proving beyond a reasonable doubt that the defendant committed the crimes charged.

Juror no. 49 characterized the crime as "reprehensible" but "absolutely" agreed that the reprehensible nature of the crime "has nothing to do with the issue of whether this defendant is guilty or not guilty," and assured the judge he could be fair. Because the issue at trial was whether the defendant committed the murder, not whether the killing of an elderly woman in her home is reprehensible, the judge correctly denied the challenge for cause.

Juror no. 12 was the soccer coach of the daughter of a Ware police officer who testified at trial. In answer to the judge's questions, he said he would be impartial in evaluating the testimony of the police witness and knew of no reason why he could not be fair. "Where, as here, the judge, who had the opportunity to observe the prospective juror, makes a determination that the juror is indifferent after exploring the grounds for a possible claim that the juror was not impartial, we cannot conclude, in the absence of any affirmative evidence to the contrary, that the judge abused his discretion." Commonwealth v. Amazeen, 375 Mass. 73, 83 (1978).

Juror no. 123 was a fire fighter but knew nothing about the case except that the defendant was charged with murder and arson. He said that the charge of arson would not affect his ability to be fair. In Commonwealth v. Ascolillo, 405 Mass. 456, 460-461 (1989), we declined to "adopt a rule that the mere fact that a prospective juror is a police officer, in the absence of a showing of prejudice or partiality, or connection with the particular facts involved at trial, would form the basis to sustain a challenge for cause." We decline to adopt a comparable rule where the prospective juror is a fire fighter in an arson case. We conclude that the judge did not abuse his discretion in denying the challenge for cause.

4. Relief pursuant to G. L. c. 278, § 33E. We have reviewed the entire record pursuant to our duty under G. L. c. 278, § 33E, and find no error that produced a substantial likelihood of a miscarriage of justice, nor any other reason to order a new trial or to reduce the defendant's murder convictions to a lesser degree of guilt.11

Judgments affirmed.