(dissenting, with whom Rubin, J., joins). I respectfully dissent because I conclude that the jury instructions were inadequate and created a substantial risk of a miscarriage of justice. I would remand for a new trial.

*548The commitment of a defendant to confinement, possibly for the rest of his life, is a most serious deprivation of liberty. The Legislature has therefore instructed that determination of sexual dangerousness, and need for secure confinement, requires a unanimous jury verdict and proof beyond a reasonable doubt. G. L. c. 123A, § 14(d). There is no dispute that jury instructions were required, and some instruction was given.1 However, the jury were not instructed on an essential element of the Commonwealth’s proof, namely, that they were required to unanimously find, by proof beyond a reasonable doubt, that the defendant was “likely to engage in sexual offenses if not confined to a secure facility” (emphasis added). G. L. c. 123A, § 1. “Sexual offenses” is a defined term covering only certain conduct. Here, determining which of the behaviors that the defendant was likely to engage in might constitute “sexual offenses” was left to the uninstructed imaginations of a jury of lay persons.

This case is directly controlled by the reasoning in Commonwealth v. Walter, 40 Mass. App. Ct. 907 (1996). There we considered jury instructions that failed to define the word “felony,” which “is an essential element of the crime proscribed by G. L. c. 266, § 18, breaking and entering in the daytime with intent to commit a felony.” Id. at 909. In that case it was critically important that the jury understand the meaning of “felony,” and the types of crimes covered by that category. Ibid. “Because the jury was not informed of the meaning of felony, ‘[t]he defendant’s fate thus turned on a layman’s definition of [felony], [This is a] technical matter[] with which laymen cannot be expected to be familiar.’ Commonwealth v. White, 353 Mass. 409, 425 (1967), cert. denied, 391 U.S. 968 (1968). See Commonwealth v. Benders, 361 Mass. 704, 708 (1972); Commonwealth v. Claudio, 418 Mass. 103, 117-119 (1994) (judge’s failure to define ‘felony’ in combination with other *549errors required reversal); Commonwealth v. Fuller, 421 Mass. 400, 411 (1995) (judge should explain meaning of technical terms where meaning is obscure and there is a possibility of confusion).” Ibid. (Emphasis added).

What an average lay juror may consider to be a sexual offense is a matter of considerable speculation, and varies from person to person depending on both subconscious and conscious influences, such as family, religion, education, culture, and other life background and experiences. The Legislature, however, has catalogued which specific sexual offenses constitute a sexual offense within the meaning of the statute. G. L. c. 123A, § 1. The Legislature did not include reference to all criminal sexual behavior and clearly intended that the jurors not self-define the term “sexual offense” for purposes of sexually dangerous person (SDP) proceedings.

In this case, the defendant, on five instances during a period of six years while he was in State prison, engaged in exhibitionism either by way of exposing himself or masturbating in the presence of one or more (usually female) individuals. Such conduct may be unlawful under G. L. c. 272, § 16,2 but violation of that statute was not a “sexual offense” within the statutory definition in effect at the time of these proceedings. G. L. c. 123A, § 1, as amended through St. 2002, c. 492.3 There was other evidence of unlawful sexual behavior by the defendant, consisting only of descriptions of the defendant’s initial rape and attempted rape in 1983 and the accompanying police reports. But the Commonwealth’s experts failed to specify which of the sexual offenses that the Legislature defined in the statute they believed the defendant would commit in the future.

“A judge should instruct the jury fairly, clearly, adequately, and correctly concerning principles that ought to guide and control their action,” Mahoney v. Gooch, 246 Mass. 567, 571 (1923); see Commonwealth v. Batchelder, 407 Mass. 752, 759 (1990), and is required to set out the elements of the offense in the charge. See Commonwealth v. Reilly, 5 Mass. App. Ct. 435, 438 (1977). This is an absolute duty that must be performed *550irrespective of whether such instructions are requested by either party. See Mahoney v. Gooch, supra at 571; Commonwealth v. Martin, 19 Mass. App. Ct. 117, 120 (1984) (“[e]ven apart from the requested instruction, the judge had the duty to state the applicable law to the jury”). Any instructions must be based on the evidence as presented at trial. See, e.g., Commonwealth v. Leftwich, 430 Mass. 865, 868 (2000) (in order to warrant submitting theory of joint venture to jury, there must be evidence sufficient to permit finding of elements of joint venture beyond a reasonable doubt).

Here, the judge identified the three principal elements of a c. 123A finding, but did not, and was not requested to, explain the words “sexual offense.” While it is axiomatic that words that retain their everyday common meaning usually need not be defined, “a judge should explain the meaning of technical terms where their meaning is obscure and there is a possibility of confusion.” Commonwealth v. Allen, 54 Mass. App. Ct. 719, 724 (2002).4

In the SDP commitment process, the words “sexual offense” do not have an everyday common meaning but, rather, have been specifically defined by the Legislature. G. L. c. 123A, § 1. The judge should have provided an explanation. See Commonwealth v. Walter, 40 Mass. App. Ct. at 909; Commonwealth v. Allen, supra at 724 (requiring explanation of the term “telecommunication services”). The failure to do so “required the jury to speculate in reaching its decision.” Commonwealth v. Niziolek, 380 Mass. 513, 527 (1980). See Commonwealth v. Kessler, 442 Mass. 770, 777 (2004) (requiring definition of “recklessly” where “there is the possibility that the jury would not realize that recklessness requires more than mere negligence”). Compare Commonwealth v. Fuller, 421 Mass. 400, 411-412 (1995) (no error in failing to define “mental disease or defect” in instruction on criminal responsibility, where instruction followed language approved by Supreme Judicial Court, and where defense experts “discussed the psychological factors in depth”).

*551I next must consider whether the error created a substantial risk of a miscarriage of justice.5 In so doing, “[w]e consider the strength of the Commonwealth’s case, the nature of the error, the significance of the error in the context of the trial, and the possibility that the absence of an objection was the result of a reasonable tactical decision.” Commonwealth v. Azar, 435 Mass. 675, 687 (2002). Because there was an enormous amount of evidence in this case of the defendant repeatedly engaging in unlawful (and repulsive) sexual behavior while in prison that, despite its criminality, did not amount to a “sexual offense” within the meaning of the statute during the relevant time, the failure to define those words was significant. See Commonwealth v. Acevedo, 446 Mass. 435, 450 (2006). Further, the evidence with respect to the likelihood to commit a defined “sexual offense” was not “strong and one-sided,” Commonwealth v. Miranda, 22 Mass. App. Ct. 10, 21 (1986), because the parties presented competing, sophisticated expert testimony. The failure to explain the words “sexual offense” required the jury to speculate as to their meaning, and presents the serious risk that the jury either misunderstood the legal meaning of the words or disregarded them entirely. Although counsel may have chosen not to request a definition for strategic reasons, “there is no reasonable tactical basis for a failure to object to a mistaken and unfavorable (to the defendant) definition of an element of the crime.” Commonwealth v. Azar, supra at 689.6

In a case such as this, where the jury were not instructed completely on the elements of the Commonwealth’s required proof, “there is a substantial risk that a person has been convicted *552for a course of conduct that [does not make him a sexually dangerous person].” Commonwealth v. Amirault, 424 Mass. 618, 647 n.21 (1997). This risk was exacerbated by the testimony at trial. Although three of the four experts offered their opinions that exhibitionism alone could not support a finding of sexual dangerousness, these opinions did not state that this was because of a limitation in the scope of the statute. Further, these opinions are not instructions. They cannot substitute for instructions. It is the judge, not experts, who instructs the jury as to matters of law. Neither of the Commonwealth’s witnesses testified as to what future behaviors, as defined by the Legislature, could be anticipated, let alone with any specific reasonable probability. The record lacks any testimony as to which sexual offenses the defendant was likely to commit. The only relevant testimony was the bare opinion by both of the Commonwealth’s experts that the defendant had a personality disorder that made him likely to commit sexual offenses. The jurors were left to guess as to what future behaviors might constitute “sexual offenses” so as to commit the defendant as a sexually dangerous person.7

I therefore conclude that the insufficient instruction resulted in a substantial risk of a miscarriage of justice, and I would remand the case for a new trial. On remand, I should note, the jury could not be instructed by providing them with the entire list of “sexual offenses” defined by the statute, any more than a jury deciding a case of breaking and entering with intent to commit a felony may be provided with a list of all felonies. Indeed, given the powerful reactions that people may reasonably have to many of the offenses described, this would be unfairly prejudicial. Rather, the law, as noted, requires that any instruction be based upon the evidence as developed at trial, compare Commonwealth v. Gonzalez, 67 Mass. App. Ct. 877, 881 (2006) (judge not required to charge the jury on a specific theory of defense if there is no rational basis for it in the evidence), and should be the product of active conversation between the judge and counsel. Cf. 6A Wash. Prac., Wash. Pattern Jury Instr. Civ. WPI 365.16 (5th ed. 2005) (for similar statute, suggesting that analogue to “sexual offense” be defined with reference to the specific *553crimes the evidence suggests the defendant is “likely to commit in the future”). I say this mindful of the trial judge’s primary role in formulating legal instructions specifically applicable to the particular issues and evidence in a case, as experienced during trial.

The failure to instruct the words “sexual offense” to the jury left them to their uninstructed imaginations in deciding this case, and thus created a substantial risk of a miscarriage of justice. I would reverse the judgment and remand for further proceedings.

After his adjudication as a sexually dangerous person, G. L. c. 123A, and commitment to the Massachusetts Treatment *539Center at Bridgewater State Hospital for a term of from one day to life, the defendant appeals. He also appeals from the denial of his motion for relief from judgment. The defendant claims (1) that the jury instructions were insufficient; and (2) that the proceedings were improperly brought because a Federal immigration detainer had been lodged against him that would preclude his release into the community. We conclude that the jury instructions, without objection and agreed to by trial counsel, were not in error and did not create a substantial risk of a miscarriage of justice. We also rule that the Federal detainer does not contradict the proceedings.

1. Procedural background. The defendant was convicted by plea in September of 1983 on two counts of assault with intent to rape, one count of assault and battery by means of a dangerous weapon, and one count of assault by means of a dangerous weapon. The defendant was committed to State prison and was paroled in 1986. While on parole, he was convicted and sentenced in New York on a property offense. He was returned to Massachusetts in May, 2002, where parole was revoked and he was returned to prison. In April, 1993, Federal authorities lodged a detainer informing of a pending order of deportation against the defendant.

Prior to the defendant’s scheduled release from prison, the District Attorney filed a petition for the defendant’s commitment under G. L. c. 123A; probable cause was found. The defendant was examined by two qualified examiners pursuant to G. L. c. 123A, § 1, and two experts of his choosing. Expert reports were filed, and a jury trial took place in December, 2003.1 The jury found the defendant to be a sexually dangerous person and committed him. On March 23, 2006, the defendant filed a motion for relief from judgment arguing that the commitment proceedings were premature and void because the immigration detainer precluded his release to general society. That motion *540was denied. He appeals from both the 2003 judgment and the 2006 denial of his motion for relief from judgment.

2. The jury trial. Evidence at the trial included testimony from the four experts as well as their written reports. The qualified examiners both opined that the defendant was a sexually dangerous person, while the defendant’s two retained experts opined that he was not. The expert testimony focused on several areas: the defendant’s underlying criminal sexual offenses; the defendant’s sexual conduct during his incarceration; assessment of the defendant’s personality disorder; and the defendant’s likelihood to reoffend, based on various protocols and actuarial models. The documentary evidence also included the grand jury minutes of the underlying 1983 criminal sexual offenses; detailed police reports describing those incidents and the complaints to the police from the victims; and nineteen disciplinary reports of the defendant’s sexually related behavior while incarcerated in Massachusetts.2

3. Jury instructions. For the reasons that follow, we conclude that there was no error in the jury instructions that would yield a substantial risk of a miscarriage of justice. First, contrary to the arguments advanced on appeal, defense counsel’s decision to accept the jury instructions would, in this case, be a reasonable *541strategic election. Second, counsel’s decision not to have the jury instructions emphasize the issue of exhibitionism by the defendant during his prison incarceration would also be a reasonable strategic election where the exhibitionism was excluded by the experts as a predicate for a finding of future sexual dangerousness under G. L. c. 123A. Third, the trial evidence concerning the defendant’s characteristics as a sexually dangerous person was strong and clear.

Against the backdrop of the trial evidence, and applying the elements that the Commonwealth must prove, we determine that under G. L. c. 123A, the issue whether the defendant was a sexually dangerous person was correctly framed in the jury instructions, and that this jury could have reached an informed determination beyond a reasonable doubt that the defendant was a sexually dangerous person under G. L. c. 123A.

We turn to the judge’s instructions, and then turn to a review of the trial record, which we conclude supports a jury verdict reflecting that each of the elements of proof under G. L. c. 123A was met. The judge instructed the jury as follows:

“So, as I have explained, the sole issue that you are called upon to decide in this case is whether the [defendant], as of the present time, is a sexually dangerous person. Our Legislature has defined the sexually dangerous person as any person who has been convicted of a sexual offense and who suffers from a mental abnormality or personality disorder which makes the person likely to engage in sexual offenses if not confined to a secure facility. Here, the Commonwealth is proceeding only under the theory of personality disorder and not mental abnormality. So to meet its burden of proof in this case, the Commonwealth must prove each of three elements beyond a reasonable doubt: first, that the [defendant] has been convicted of a sexual offense; second, that he suffers from a personality disorder, and third, that as a result of the personality disorder, he is likely to engage in sexual offenses if not confined to a secure facility. Those are the three elements.”

On the first element, with respect to the defendant having been convicted of a sexual offense, the jury heard evidence concerning the defendant’s convictions on rape and attempted rape indictments. The convictions arose from the defendant’s attacks on two *542women on one day in 1983. Both victims were strangers to the defendant; he accosted both women and, with force and violence, raped one woman and attempted to rape the other woman.3

Beyond these convictions for sexual offenses, there was evidence that the defendant engaged in inappropriate sexual behavior while incarcerated from 1994 to 1999. Prison disciplinary reports were filed against the defendant for five separate incidents. Each incident involved the defendant exposing his penis or masturbating in the presence of a female nurse, prison counselor, or a correction officer. The defendant later described these incidents as “tum[ing him] on” or “arous[ing him].” There were also prison disciplinary reports concerning aggressive behavior by the defendant when he threw feces at a guard, and attacked another inmate with a padlock.

On the second element of personality disorder or mental abnormality, the judge’s instructions were explicit, unequivocal, and correct that the Commonwealth was relying on proof that the defendant suffered from a personality disorder. This part of the jury instructions was consistent with all the expert psychiatric and physiological evidence presented. Specifically, from the testimony of all four experts — the two qualified examiners for the Commonwealth and the two defense experts — it was clear that the personality disorder of the defendant at issue was an antisocial personality disorder. Both of the Commonwealth’s qualified examiners opined that the defendant met the criteria for antisocial personality disorder. Both defense experts acknowledged that the defendant exhibited the characteristics of antisocial personality disorder, except for the criterion that the defendant manifested this disorder before the age of fifteen. Even accepting the defense experts’ reservation because of the missing diagnostic criterion concerning the defendant’s behavior before the age of fifteen, all four experts agreed that the defendant suffered from antisocial personality disorder. Thus, the judge’s instructions *543correctly directed the jury to consider whether the Commonwealth had proved that the defendant had a personality disorder. Given the evidence, we are not persuaded that there was any likelihood that there would be potential jury misunderstanding concerning the legal standard, or jury confusion concerning the evidence as applied to this second element. In sum, we discern no error that would give rise to a substantial risk of a miscarriage of justice arising out of this part of the jury instruction concerning personality disorder.

The third and final element of the jury instructions was “that as a result of the personality disorder, [the defendant] is likely to engage in sexual offenses if not confined to a secure facility.” Both of the Commonwealth’s qualified examiners concluded that the defendant’s antisocial personality disorder, his prior rape and attempted rape convictions, and the pattern of his inappropriate sexual behavior (exhibitionism) while in prison supported the opinion that the defendant would re-offend and commit sexual offenses. The first qualified examiner, Dr. Tomich, based his ultimate opinion that the defendant was sexually dangerous on the fact that the victims were strangers whom the defendant seized from public places and assaulted with force and weapons (knife and razor). Dr. Tomich also based his opinion of future sexual dangerousness on the defendant’s proclivity for deviant sexual arousal, as reflected in the defendant’s sexual and aggressive conduct during incarceration.4 The second Commonwealth qualified examiner, Dr. Feldman, also concluded that the defendant was likely to be sexually dangerous in the future. In support of this opinion, Dr. Feldman focused on the fact that the original offenses were perpetrated on anonymous victims, with violence, and with weapons. Dr. Feldman’s testimony also considered the defendant’s continuing deviant sexual arousal and aggression, and cited the defendant’s unwillingness to take responsibility for his criminal acts, his lack of remorse, and his failure to complete sex offender treatment.

*544Both defense experts were of the contrary opinion and concluded that the defendant would not be likely to re-offend and would not be sexually dangerous in the future. Dr. Plaud reasoned that the defendant was at low risk to re-offend based on an actuarial test linked to the defendant’s age. Dr. Plaud also considered the lack of offenses committed after the rape convictions. The other defense expert, Dr. Bard, concluded that the defendant was not likely to re-offend based on the application of three actuarial tests, which took into account factors such as the defendant’s age and number of convictions.

The jury, however, could determine that the opinions of the qualified experts for the Commonwealth were more compelling and persuasive. This is particularly so in that while both defense experts opined against the prospect of future sexual dangerousness, they acknowledged that the defendant demonstrated many of the elements of an antisocial personality, that his prior sexual offenses manifested violence and aggression, and that his sexually inappropriate behavior continued during his prison term.

In sum, throughout the trial, there was evidence to prove the third element under G. L. c. 123A, that the defendant was likely to continue to engage in sexual offenses if not confined. The third part of the instructions, albeit short, was clear on this element.5

The defendant did not request that the judge instruct the jury that the defendant’s exhibitionism was not a predicate offense for future dangerousness consideration.6 Nor did the defendant’s counsel subsequently object to the judge’s omission of such a spontaneous instruction. This defense stance, as previously noted, would be a justified litigation strategy because any such reference in the legal instructions to the defendant’s pattern of exhibitionism might have yielded an overly predominant focus on this issue at this point in the trial — especially since, *545adverse to the defense, these incidents were more recent in time (1994-1999), in contrast to the much older (1983) rape-related offenses.

Despite the lack of objection at trial, the defendant nevertheless argues on appeal that the instructions were inadequate because exhibitionism was not a defined predicate sexual offense under G. L. c. 123A, § 1, at the time of the trial.7 Thus, the defendant argues, the jury may have been confused and considered the five incidents of exhibitionism, when he exposed himself and masturbated, as potential sexual offenses that he would be likely to continue to engage in — conduct not then covered by G. L. c. 123A. The record does not support that proposition. To the contrary, the expert evidence was clear that exhibitionism would not trigger a finding of sexual dangerousness under G. L. c. 123A.8 Given the testimony and reports of the experts, the jurors could not plausibly have been confused *546by the lack of an instruction on exhibitionism. Furthermore, during the direct testimony of the first qualified examiner, the trial judge convened a side bar conference and instructed counsel that the prison reports should be referred to as “incidents” or some equivalent term, rather than as “offenses.”

Finally, we note, contrary to the suggestion in the dissent, that the defendant does not focus his appellate challenge on a claim that a more thorough definition of sexual offense should have been given. The defendant did not request that the instructions include a list of the specific crimes enumerated in the statutory definition of sexual offense. G. L. c. 123A, § 1. Thus, we do not see how the failure to provide additional explanations in the jury charge gave rise to error and a resulting substantial risk of a miscarriage of justice. In a case such as this, a jury does not need, and absent a specific instruction request with supporting reasons therefore, would generally not be given, a complete list of the sexual offenses set forth in G. L. c. 123A, § 1. Certainly the jury may apply their own common sense as to what is a sexual offense, particularly when the entire trial evidence was so directed — with exhibitionism being specifically excluded in the expert evidence testimony. See note 8, supra. Cf. Commonwealth v. Hosman, 257 Mass. 379, 385-386 (1926); Commonwealth v. Muckle, 59 Mass. App. Ct. 631, 643 (2003).

For the foregoing reasons, we do not discern error in the jury instructions such as would give rise to a substantial risk of a miscarriage of justice, and warrant reversal. “ ‘A trial judge has wide latitude in framing the language to be used in jury instructions’ as long as the instructions adequately explain the applicable law.” Kelly v. Foxboro Realty Assocs., LLC, 454 Mass. 306, 316 (2009), quoting from Jacobs v. Pine Manor College, 399 Mass. 411, 414 (1987). “The test of the charge is the impression created *547by it as a whole.” Commonwealth v. Kelley, 359 Mass. 77, 92 (1971). In this case, based on the instructions, the jury would have been informed that they were to determine whether the Commonwealth had proved beyond a reasonable doubt the three elements under G. L. c. 123A, that is, prior sexual offenses had been committed by the defendant; the defendant suffered from a personality disorder; and the defendant was likely to commit sexual offenses in the future.

4. Federal detainer. We reject the defendant’s argument that because he is subject to a detainer order issued by the Federal government, he cannot be committed pursuant to G. L. c. 123A proceedings. The decision to execute a deportation order rests entirely with the Federal authorities, who have the discretion to “abandon the endeavor” at any time, whether “for humanitarian reasons or simply for . . . convenience.” Reno v. American-Arab Anti-Discrimination Comm., 525 U.S. 471, 483-484 (1999). Thus, there is no guarantee that the lodging of a Federal detainer will accomplish the Legislature’s purpose under c. 123A: to prevent the release of “persons currently incarcerated for sexual offenses who are about to be released into the community but who, because they are sexually dangerous, are likely to commit another sexual offense.” Commonwealth v. McLeod, 437 Mass. 286, 291 (2002). See Commonwealth v. Ferreira, 67 Mass. App. Ct. 109, 113 (2006). Nor is there any support for the defendant’s suggestion that the deportation order and Federal detainer preempt State action under c. 123A. The defendant, until actually deported, remains subject to the laws of the Commonwealth, see Plyler v. Doe, 457 U.S. 202, 215 (1982), and no procedure has been initiated by the Federal authorities to intervene in the c. 123A proceedings.

Judgment affirmed.

Order denying motion for relief from judgment affirmed.