¶1At issue is the power and authority of a trial judge to accept, over the Commonwealth’s objection, a plea to murder in the second degree from a defendant indicted for murder in the first degree. In this case, the plea was accepted over objection and in the face of sufficient evidence to warrant submitting the matter to the jury on the charge of murder in the first degree. The Commonwealth asserts that the judge’s exercise of such power violates art. 30 of the Massachusetts Declaration of Rights.
¶2Ventry Gordon, the defendant, was charged in two indictments with murder in the first degree.*
¶3As a preliminary matter, we note that the petition for relief pursuant to G. L. c. 211, § 3, is properly before us. The parties agree that the judge’s acceptance of the pleas to murder in the second degree constitutes a dismissal of the indictments of murder in the first degree. If the judge had, in fact, actually dismissed the charge of murder in the first degree, the Commonwealth could have appealed pursuant to Mass. R. Crim. P. 15 (b), as amended, 397 Mass. 1225 (1986). The judge, however, did not do so. Nor was the judge’s action taken in response to the types of motions contemplated in Mass. R. Crim. P. 13 (c), 378 Mass. 871 (1979), and rule 15 (b). Because there was no appellate remedy to determine the correctness of the judge’s actions, the district attorney properly sought relief pursuant to G. L. c. 211, § 3.
¶4*500We have observed that, “[i]f a valid complaint or indictment is dismissed prior to a verdict, finding or plea, without an evidentiary hearing and over the objection of the Commonwealth ‘[t]he effect ... is like that of quashing or entering a nolle prosequi of an indictment.’ Commonwealth v. Bressant, 126 Mass. 246, 247 [1879]. There is, indeed, serious doubt as to the power of a court to enter such an order.” Commonwealth v. Brandano, 359 Mass. 332, 334-335 (1971). The reason for the doubt expressed in Brandanois the long-standing proposition that the decision to nol pros a criminal case is within the discretion of the executive branch of government, free from judicial intervention. See Shepard v. Attorney Gen., 409 Mass. 398, 401 (1991); Burlington v. District Attorney for the N. Dist., 381 Mass. 717, 721 (1980); Manning v. Municipal Court of the Roxbury Dist., 372 Mass. 315, 318 (1977); Commonwealth v. Tuck, 20 Pick. 356, 366 (1838). In fact, as far back as 1806 this court has held that a nolle prosequi cannot be entered over the Commonwealth’s objection. See Commonwealth v. Wheeler, 2 Mass. 172 (1806). See also Commonwealth v. Hart, 149 Mass. 7, 8 (1889) (“Only an attorney authorized by the Commonwealth to represent it has authority to declare he will not further prosecute a case in behalf of the Commonwealth. A court is not a prosecuting officer .... Its office is judicial, — to hear and determine between the Commonwealth and the defendant”); Commonwealth v. Andrews, 2 Mass. 409, 414 (1807). We can see no distinction between the judge’s action in this case and a judge’s attempt to nol pros a valid indictment. In both situations, the judge has exercised discretionary decision-making power to decide whether a complaint, legally valid, should be pursued. As with the nolle prosequi, the prosecutor’s pretrial discretion to dismiss a valid complaint is essential to maintaining the balance integral to a properly functioning adversary system.
¶5The district attorney is the people’s elected advocate for a broad spectrum of societal interests — from ensuring that criminals are punished for wrongdoing, to allocating limited resources to maximize public protection. In this case, the dis*501trict attorney apparently decided that the public interest would be served by convictions of murder in the first degree. The judge’s action short-circuited the adversary process by silencing the people’s elected voice. Without any legal basis for his ruling, the judge preempted the Commonwealth’s presentation of its case. That action effectively usurped the decision-making authority constitutionally allocated to the executive branch.
¶6*502For these reasons, the judge was mistaken in relying on a dictum in District Attorney for the Suffolk Dist. v. Watson, 381 Mass. 648 (1980), in asserting this power. Watsonconcerned the constitutionality of the death penalty. In discussing the inherent arbitrariness in inflicting capital punishment, we noted that various opportunities for discretion arise throughout the handling of a criminal matter. Thus, we observed that “the judge may dismiss the first degree murder charge, in his sole discretion, pursuant to accepting a plea of guilty to a lesser offense.” Id. at 668. This isolated dictum, in the middle of a case concerned with a completely different set of issues, cannot support the judge’s action. Although the remark did not explicitly state that the discretionary power to dismiss applies only in the context of a plea agreement to which a prosecutor has consented, we think that qualification is implicit.
¶7We emphasize that this case does not involve a dismissal of an indictment on a legal basis. The district attorney is not arguing that the court lacks authority to dismiss indictments for insufficient evidence before the grand jury, see Commonwealth v. McCarthy, 385 Mass. 160, 163 (1982), or because evidence before the grand jury was not fairly presented, see Commonwealth v. O’Dell, 392 Mass. 445 (1984), or because the prosecution is barred by principles of double jeopardy, see Angiulo v. Commonwealth, 401 Mass. 71, 79-80 (1987), or for insufficiency of the evidence to be presented at trial, see Rosenberg v. Commonwealth, 372 Mass. 59 (1977). Nor is the power asserted by this judge analogous to a judge’s authority to order a finding of guilty of a lesser included offense after a jury has handed down a verdict, see Mass. R. Crim. P. 25 (b) (2), 378 Mass. 896 (1979), or the authority to revise and revoke a sentence, see Mass. R. Crim. P. 29, 378 Mass. 899 (1979).
¶8In sum, in the absence of a legal basis for taking a plea to a lesser included offense, the judge may not preclude the Commonwealth from submitting its case to a jury. Neither court congestion nor judicial economy justifies a judge in taking a plea to a lesser included offense over the Commonwealth’s objection. On the record before us, there is no legal basis for not permitting the Commonwealth to try to obtain a conviction for murder in the first degree.
¶9The defendant also argues that, even if this court decides, as we have, that the judge had no power to accept his plea to a lesser included offense over the Commonwealth’s objection, retroactive application of that decision to him would violate the due process and ex post facto provisions of both the State and Federal Constitutions. We reject this contention. Unlike those cases in which the possibility of prospective application arises, this opinion does not in any way announce a “new rule of law.” See Hanover Shoe, Inc. v. United Shoe Mach. Corp., 392 U.S. 481, 496 (1968); Commonwealth v. Bray, *504407 Mass. 296, 303 (1990). The judge had no power to accept this plea.
¶10For the foregoing reasons, judgment is to enter vacating the order of the Superior Court accepting the defendant’s pleas of guilty to murder in the second degree. Trial is to proceed in the Superior Court on the indictments for murder in the first degree.
¶11So ordered.
¶12 Article 30 of the Massachusetts Declaration of Rights provides: “In the government of this Commonwealth, the legislative department shall never exercise the executive and judicial powers, or either of them: the executive shall never exercise the legislative and judicial powers, or either of them: *499the judicial shall never exercise the legislative and executive powers, or either of them: to the end it may be a government of laws and not of men.”
¶13He also pled guilty to an indictment charging armed robbery.
¶14We take this opportunity to remind judges that they are not to participate as active negotiators in plea bargaining discussions. See Commonwealth v. Kelleher, 28 Mass. App. Ct. 915 (1989); Commonwealth v. Damiano, 14 Mass. App. Ct. 615, 622 n.13 (1982); 3 ABA Standards for Criminal Justice § 14-3.3 (2d ed. 1982 Supp.); Note, Judicial Plea Bargaining, 19 Stan. L. Rev. 1082 (1967). Concerns about judicial involvement in plea bargaining have centered around the effect on the judge’s subsequent ability to evaluate the voluntariness of the agreement, the potential coercive impact on the defendant, and the effect on public respect for the court’s impartiality. See Note, The Unconstitutionality of Plea Bargaining, 83 Harv. L. Rev. 1387, 1392 (1970); Note, Judicial Plea Bargaining, supra at 1088-1091.
¶15The defendant contends that Mass. R. Crim. P. 12 (a), 378 Mass. 866 (1979), provides the judge with discretion to accept his plea. Rule 12 (a) reads in part: “A defendant may plead . . . guilty ... to any crime with which he has been charged and over which the court has jurisdiction. . . . A judge may refuse to accept a plea of guilty . . . .” (Emphasis added.) The italicized portion of the rule makes clear that the defendant can plead *503guilty only to those crimes with which he has been charged. Moreover, Mass. R. Crim. P. 12 (b), 378 Mass. 866 (1979), is the provision authorizing exchanges of guilty pleas for charge concessions. Nothing in that rule contemplates a judge’s participation in such negotiations.
¶16For similar reasons, the defendant’s reliance on Commonwealth v. Watson, 393 Mass. 297 (1984), is misplaced. In that case, we upheld the judge’s refusal to accept the defendant’s plea to a lesser included offense, finding “no abuse of discretion.” Id. at 301. However, the plea was offered after the close of the Commonwealth’s case. No preclusion of a legally valid prosecution was involved. See Commonwealth v. Nessolini, 19 Mass. App. Ct. 1016, 1017 (1985).
¶17The dissent’s portrayal of our opinion as requiring a statement of reasons for the judge’s action mischaracterizes our conclusion. Our holding is not based on the judge’s failure to state his reasons for accepting the plea. What we said is that the judge lacked authority to take the plea to the lesser included offense. The judge’s action usurped the decision-making authority of the executive branch of government.
¶18In view of our decision, the defendant may, on motion, move to withdraw his plea to armed robbery. If the defendant so moves, the motion should be allowed.