¶1A jury in the Superior Court convicted the defendant on two indictments charging murder, finding in each case that he had acted with deliberate premeditation and extreme atrocity or cruelty, and was guilty of felony-murder (with armed robbery as the predicate felony). Represented by new counsel on appeal, the defendant argues error in (1) the denial of his motion to suppress his statements to the police and photographs taken by them of his athletic shoes; (2) the admission of deoxyribonucleic acid (DNA) evidence by an expert witness; and (3) the denial of his motion for a new trial. We conclude that there is no error and no basis for granting relief under G. L. c. 278, § 33E.
¶2It is not necessary to set forth in detail" the findings that the jury could have made based on the Commonwealth’s evidence.
¶31. We reject the defendant’s argument that the motion judge improperly denied his motion to suppress his oral and written statements to the police.
¶4The judge held an evidentiary hearing on the motion to suppress, and he entered a memorandum of decision in which he made findings of fact and conclusions of law. The judge’s findings of fact are supported by the evidence that he found credible, and we accept them. See Commonwealth v. Robinson, 399 Mass. 209, 215 (1987), quoting Commonwealth v. Moon, 380 Mass. 751, 756 (1980). The judge found that the defendant went voluntarily to the police station. When he was questioned there, the defendant was not restrained in any way, and there was no probable cause to arrest him. At the time of the interview, the defendant was not the focus of the investigation; the police were still investigating the killings and were talking to numerous people (the defendant among them) who may have had some contact with Hope. The interview was relaxed and amicable, not confrontational, and the defendant willingly answered questions asked of him. (The judge found that “[t]he questioning was influenced in its contours by the defendant and his answers.”) The defendant read and signed his written statement, which contained no confession. When the interview was completed, the police offered the defendant a ride back to work. The defendant declined the offer, and he was allowed to leave the police station.
¶5The judge applied the factors set forth in Commonwealth v. *657Bryant, 390 Mass. 729, 737 (1984),
¶62. During the interview, the police asked the defendant *658whether they could look at the soles of his athletic shoes. The defendant responded by lifting his feet so the police could view the bottoms of the shoes. A police photographer was brought in to photograph the shoes. The photographer suggested that the shoes should be removed so he could more easily obtain photographs. The defendant agreed to do so and took his shoes off, and, when the photographer finished, the shoes were returned to the defendant. The defendant argues that the shoes were “seized” by the police without his consent and that the photographs, therefore, were unconstitutionally obtained. The defendant argues that all evidence derived from the photographs should have been suppressed.
¶7The judge found that the police had seen footprints in the victims’ apartment and were collecting photographs of the bottoms of numerous shoes to compare with those footprints. The judge also found, and concluded, that taking photographs “of the sole[s] of [the defendant’s] shoes [was] agreed to [by the defendant and] was not the result of any coerced or involuntary action [on the defendant’s part]. He freely and openly took off his shoes so they could be photographed.” The judge’s findings and conclusions are supported by the evidence. The police examination of the soles of the defendant’s athletic shoes did not constitute a search, see Commonwealth v. Billings, 42 Mass. App. Ct. 261, 264-266 (1997), and, because the defendant consented to removing his shoes so they could be photographed, there was no illegal seizure. The photographs were part of the interview process which, as we have concluded, violated no constitutional rule. This aspect of the defendant’s motion to suppress was properly denied by the motion judge.
¶83. The Commonwealth introduced the expert testimony of Dr. Robin Cotton, the laboratory director of Cellmark Diagnostics Laboratories (Cellmark), a recognized forensic laboratory located in Germantown, Maryland. Dr. Cotton testified about Cellmark’s DNA testing (by means of the polymerase chain reaction [PCR] method) of DNA obtained from bloodstains found in the victims’ apartment and the statistical frequencies of matches between the DNA derived from the bloodstains and the DNA of the victims and the defendant.
¶9Before Dr. Cotton was called to the witness stand, the *659defendant’s trial counsel objected to her testimony on the basis that she was not the actual staff scientist who had conducted the initial reviews of the analysts’ reports; rather, in reaching her conclusions, she had reviewed the records, analysis, and results of Cellmark analysts who had conducted the testing, and of other Cellmark staff scientists (or reviewers) who had conducted the initial review of the analysts’ work. Trial counsel argued that Dr. Cotton’s testimony could not be admitted unless the Cellmark analysts involved in the testing were also called to testify. The judge held an evidentiary voir dire at which Dr. Cotton testified and was cross-examined. The judge overruled trial counsel’s objection, concluding that Dr. Cotton was a qualified expert in the field of DNA testing, who, although not the initial staff scientist who reviewed the analysts’ work, had conducted “an independent review of the empirical data separate and apart from the review undertaken by the [analyst]” that “encompasse[d] all that the original [staff scientist had done].” The judge then permitted Dr. Cotton to testify to her opinions under the rule that “an expert [may] base an opinion on facts or data not in evidence if the facts or data are independently admissible and are a permissible basis for an expert to consider in formulating an opinion. [This] . . . eliminate^] the necessity of producing exhibits and witnesses whose sole function is to construct a proper foundation for the expert’s opinion.” Department of Youth Servs. v. A Juvenile, 398 Mass. 516, 531 (1986). See Commonwealth v. O’Brien, 423 Mass. 841, 851-852 (1996), S.C., 432 Mass. 578 (2000). The defendant’s appellate counsel now raises an entirely new basis to exclude Dr. Cotton’s testimony. He argues that the testimony should have been excluded because the DNA testing kits used by Cellmark, and its database for formulating statistical frequencies, were not shown to be scientifically reliable. We reject the argument.
¶10To preserve objections to DNA analysis of the type in issue, a defendant must file an appropriate pretrial motion stating the grounds for the objections and request a hearing in accordance with the principles set forth in Canavan’s Case, 432 Mass. 304, 309-312 (2000), and Commonwealth v. Lanigan, 419 Mass. 15, 24-27 (1994). The defendant’s trial counsel made no such motion in this case, apparently for tactical reasons. Dr. Cotton’s *660testimony was cumulative of the evidence presented by the Commonwealth’s serologist (although it did focus on the identifications with more particularity than those obtained by blood typing). Trial counsel also may have considered Cell-mark’s reputation for quality forensic work, Dr. Cotton’s position at Cellmark (laboratory director), and the fact that, prior to trial, in Commonwealth v. Rosier, 425 Mass. 807, 813-817 (1997), we had upheld similar DNA testing by Cellmark and its database formulations. Further, trial counsel likely anticipated the defendant’s trial testimony, namely, his admission that he had bled all over Hope’s apartment from cuts on his hands.
¶11In addition, the defendant’s appellate counsel conceded at oral argument on the appeal that no expert evidence exists to challenge the scientific validity of Dr. Cotton’s testimony or the conclusions reached by Cellmark. As such, the objections made in the defendant’s brief lack factual foundation. In view of the only objection made at trial prior to Dr. Cotton’s testimony, and no persuasive showing here that the testing was unreliable, the judge properly admitted Dr. Cotton’s testimony under the rule stated in Department of Youth Servs. v. A Juvenile, supra.
¶124. The trial judge properly denied the defendant’s motion for a new trial after an evidentiary hearing. The defendant’s motion was based on allegedly newly discovered evidence suggesting that the police had planted a knife in the defendant’s bedroom during the execution of a search warrant. In support of the motion, the defendant offered the testimony of the owner of the house where the defendant lived. In her affidavit, the owner *661claimed that, on the day or days before the police had claimed to have seized a steak knife with bloodstains on it from under a mattress in the defendant’s bedroom while executing a search warrant, the police, in her presence and with her assistance, had conducted a warrantless search of the defendant’s bedroom, including searching under the defendant’s mattress and bed frame which revealed nothing.
¶13In her memorandum of decision on the motion, the judge found the owner’s evidence completely untruthful, noting that her testimony contradicted her affidavit, and that both her affidavit and testimony were shown by cross-examination to be false. As the judge noted, the witness ‘‘ self-immolat [ed] ’ ’ on the stand. The judge’s findings rejecting the motion are based on credibility, and, as such, are final and conclusive on the issue. See Commonwealth v. Bernier, 359 Mass. 13, 16 (1971), and cases cited.
¶145. After reviewing the record under G. L. c. 278, § 33E, we conclude that the interests of justice do not require a reduction in the murder verdicts or a new trial.
¶156. The judgments of conviction and the order denying the defendant’s motion for a new trial are affirmed.
¶16So ordered.
¶17The trial judge, in her memorandum of decision on the defendant’s motion for a new trial, aptly described the Commonwealth’s evidence as presenting an overwhelming case for the defendant’s convictions.
¶18In his statements to the police, the defendant denied having been at Hope’s apartment on the night of the murders and stated that he had cut his right hand while slicing tomatoes on the day following the murders. At trial, the Commonwealth used the defendant’s statements to contradict his testimony that he had cut his hand at work on the day before the murders.
¶19As to the second factor set forth in Commonwealth v. Bryant, 390 Mass. 729, 737 (1984) (whether the investigation had begun to focus on the suspect, including whether there was probable cause to arrest the suspect), see Commonwealth v. Morse, 427 Mass. 117, 125 n.6 (1998), where we expressed doubt whether that factor was ever relevant to the Miranda inquiry.
¶20The defendant testified that he obtained a cut on his hand during an encounter with an intruder in Hope’s apartment. He testified that, on the night of the murders, he went to visit Hope’s landlord and noticed that the door to Hope’s apartment was ajar. After ringing the doorbell without response, he entered the apartment where he claimed that he was hit from behind by a man wearing a black mask and gloves, who was holding a knife. The man approached the defendant with the knife and cut the defendant’s hand with it as the defendant raised his hands up in his own defense. The man then ran out the door. The defendant testified that his hand bled not only from the cut he received from the masked intruder, but also from a cut to his hand that he had sustained at work.