The defendant, Cullen, appeals from his convictions in the Superior Court on two counts of assault with intent to murder, two counts of assault and battery by means of a dangerous weapon, and one count of unlawful carrying of a firearm. Cullen’s sole defense at his jury-waived trial was lack of criminal responsibility as defined in Commonwealth v. McHoul, 352 Mass. 544 (1967), i.e., that he lacked substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of law. The issue on appeal is whether, as matter of law, the Commonwealth’s evidence sufficed to support the trial judge’s determination that Cullen was criminally responsible for the shootings. We determine that the evidence presented by the Commonwealth provided a legally sufficient basis for a finding of criminal responsibility. We cannot invade the province of the fact finder by substituting *645the view of an appellate court on questions concerning the credibility of witnesses or the weight of evidence. The Superior Court’s judgments are affirmed.
After midnight on February 5, 1983, while driving past 338 Central Avenue in Milton, Officer Paul Nolan heard a “loud bang” at the rear of his marked cruiser. He called the station for a back-up, pulled over, and stepped out of his car, asking Cullen, who was standing in the driveway of his home, if he had seen what had happened. Cullen had recently returned home from six or more hours spent drinking with a friend. Cullen did not respond to Nolan’s inquiry. However, as Nolan came within twelve feet of him, repeating the question, Cullen drew a handgun, for which he had no license, from his waistband and began shooting at Nolan. The first bullet broke Nolan’s left arm. Another caught him in the knee as he dove for cover near a car parked in the Cullen driveway. Yet another shot passed through Nolan’s shirt and jacket without causing injury. Cullen then apparently disappeared behind his house, reemerging less than a minute later and firing upon Officer Charles Paris, who, by that time, was kneeling beside Nolan and radioing for help. Paris sustained a bullet wound in his back, which, as Paris testified, was turned toward Cullen at the time. Another shot damaged the portable radio on Nolan’s hip. Turning, Paris fired four times in the direction of Cullen’s muzzle flashes. Cullen fled.
Additional police then arrived and almost immediately received a radio report of an attempted break-in at 352 Central Avenue, the residence of a former lawyer of Cullen’s. Officer Michael Breen found Cullen at the foot of the porch stairway at this address and, with service revolver drawn, ordered: “Frankie, give it up.” Cullen then tinned his back to Breen and placed his hands on the side of the house. As Breen approached, Cullen began to back away from the house. Believing him about to flee, Breen grabbed Cullen from behind, simultaneously restraining him and searching for the handgun. Both men fell to the ground. Officer Paris, arriving at the scene, handcuffed Cullen’s wrists behind his back. Subsequently, Cullen “began to thrash about from left to right,” which gyrations *646soon revealed to the police a handgun under his back approximately at his beltline. Through expert testimony, the Commonwealth presented evidence of the gun’s make and also of the fact that Cullen had reloaded it before being apprehended.
Cullen did not testify at trial, nor did he substantially contest these facts. Instead, through two psychiatrists, he offered evidence of his lack of criminal responsibility.1 According to one psychiatrist, Cullen said the Milton police were “out to get him,” that they, and other police departments from eastern Canada to New York City, had kept him under twenty-four hour surveillance for more than seven years. His phone was bugged, he averred. The police played “mind games” with him that “let him kill people,” and caused “pins and needles attacks” in various parts of his body. The police interfered with his love life — which Cullen said potentially included five hundred women whom he knew to be attracted to him — by telling women that he was a sex pervert.2 The psychiatrist testified that Cullen admitted that he had purchased the handgun on the street to protect himself from the police, and likewise threw a rock at the police cruiser and shot Nolan and Paris in self-defense. He told the psychiatrist that, while it would have been easy for him to kill the wounded Nolan, he refrained from doing so, intending only to “put him out of service.” Cullen insisted that he ran to his lawyer’s house only because “he was sure that the police would not kill him in front of . . . his attorney.”
Both psychiatrists concluded, on the basis of slightly different diagnoses, that Cullen lacked criminal responsibility under the McHoul test, suggesting that the appropriate diagnostic labels for Cullen’s condition might be “schizophrenia, paranoid type” and “erotomania,” or a “paranoid delusional system.” Confronted at trial with an EEG report from Bridgewater *647revealing minimal physical abnormalities, one expert changed her diagnosis to include the possibility of an organic psychosis.
Obviously, the trial judge rejected Cullen’s insanity defense. Thus the question we must decide is whether, on the basis of all the evidence, viewed in a light most favorable to the prosecution, a rational trier of fact could have found Cullen to be criminally responsible beyond a reasonable doubt.3 Commonwealth v. Latimore, 378 Mass. 671, 677-678 (1979); Commonwealth v. Shelley, 381 Mass. 340, 346 (1980); Jackson v. Virginia, 443 U.S. 307, 318-319 (1979). A more extensive review of the evidence is available under G. L. c. 278, § 33E, but this court has no authority under that statute; moreover, the statute applies only in capital cases such as Commonwealth v. Guiliana, 390 Mass. 464 (1983).
Cullen does not suggest that the Commonwealth’s evidence of criminal responsibility was insufficient at the close of the Commonwealth’s case in chief. Until Cullen raised the insanity defense, the prosecution was entitled to rely on the “presumption of sanity,” that is, the rule that, unless a criminal defendant asserts the insanity defense, the Commonwealth is not obliged affirmatively to prove sanity beyond a reasonable doubt as an element of its case. Commonwealth v. Kostka, 370 Mass. 516 (1976). Cullen argues instead that the Commonwealth’s evidence deteriorated between the close of the Commonwealth’s case and the close of all the evidence, and that therefore a required finding of not guilty by reason of insanity should have been entered at the close of all the evidence. Commonwealth v. Kelley, 370 Mass. 147, 150 & n.1 (1976). He argues that following the expert psychiatric testimony that he was insane under McHoul standards the Commonwealth’s case lacked sufficient evidence to satisfy its now increased burden of proving *648sanity beyond a reasonable doubt. Cullen points to the Commonwealth’s failure to offer expert or lay testimony on the sanity issue as an indication that this heightened burden of proof has not been satisfied. The Commonwealth did introduce affirmative evidence of sanity in Commonwealth v. Lunde, 390 Mass. 42 (1983), and Commonwealth v. Werner, 16 Mass. App. Ct. 686 (1983), in which guilty verdicts were sustained in spite of undisputed psychiatric diagnoses of insanity.
The trier of fact is not, of course, obliged to regard even unanimous expert opinion as conclusive on the issue to which it is addressed. Commonwealth v. Lunde, 390 Mass. at 47, and cases cited. Here, for example, the trial judge could have disbelieved the expert testimony or accorded it less weight either because the psychiatrists’ diagnoses were not in complete agreement or because the judge believed the experts’ interviews with Cullen to have been too brief or too remote in time from the shooting.4 Commonwealth v. Robinson, 14 Mass. App. Ct. 591, 595-596 (1982).
Cullen attempts to distinguish the sufficiency of the sanity evidence in this case from the sanity evidence held sufficient in cases such as Lunde, and Werner, supra. He argues that evidence offered by the Commonwealth in Lunde showed Lunde’s capacity to discriminate between victims, his calm and rational demeanor, and selection of a particular attorney following an incident in which he shot his brother-in-law more than a dozen times. Cullen points out that, in Werner, the Commonwealth offered evidence that after an unprovoked, fatal stabbing of a teenage girl in a Springfield bus terminal, Werner hid both his weapon and himself, exhibited a calm demeanor when captured, and made two detailed and coherent drafts of a confession in which he admitted to planning such a murder. In this case, Cullen suggests, no such demeanor or other evidence of sanity exists. We disagree.
The trial judge was entitled to draw inferences of sanity from evidence of Cullen’s behavior at the time of the shooting. *649Commonwealth v. Amaral, 389 Mass. 184, 192 (1983). We must therefore determine whether the Commonwealth’s case in chief contained facts legally sufficient to support a reasonable inference of sanity beyond a reasonable doubt.
Cullen’s admission to one of the experts that for six or more hours before the shooting he had been drinking with a friend could support an inference that voluntary consumption of alcohol, not insanity, caused his violent behavior. Cullen’s prior steady employment as a crane operator, a position he lost when the work was discontinued, and not because of erratic behavior, also supports an inference of criminal responsibility. Likewise, the facts that Cullen was carrying a gun, hurled a rock at the cruiser, waited for Nolan to come close to him before shooting, and returned from the rear of his house to fire upon Paris, support inferences of preparation and deliberation. Cullen’s assertion that he could have killed Nolan, but refrained from doing so, his dash to his former attorney’s home, and his eventual surrender to Officer Breen,5 may all indicate to the trier of fact that Cullen could appreciate the criminality of his conduct. Further, while Cullen’s post arrest “thrashing” could suggest the raging of a madman, it could also be attributed to his determination to reach the gun still beneath him.
The potential of a fact to support more than one reasonable inference does not warrant our substituting our judgment for that of the trier of fact, who was in the best position to evaluate the evidence he heard first hand.
Judgments affirmed.
Cullen’s conversations with the experts may be admitted insofar as they provide insight into his mental condition. Blaisdell v. Commonwealth, 372 Mass. 753, 766 (1977).
Cullen had previously been arrested several times for lewd behavior, including indecent exposure. He was on probation for armed robbery at the time of the shootings. His belief that the police were watching him may have a rational basis.
At the close of all the evidence defense counsel asked the trial judge to “find the defendant not guilty under the guidelines of Commonwealth v. McHoul” because the Commonwealth did not offer any evidence to rebut the “presumption” that Cullen lacked criminal responsibility at the time the act was committed. We accept this request as a motion for a required finding of not guilty under Mass.R.Crim.P. 25, as amended, 389 Mass. 1107 (1983) [added 25(c)]. In any case there is no doubt as to the basis on which the case was tried. See Commonwealth v. Lunde, 390 Mass. 42, 47 n.7 (1983).
Further, Cullen had no prior history of psychiatric treatment except one referral to a residential treatment program, possibly for psychiatric reasons, some twenty-five years earlier. There was little evidence to corroborate the “facts” Cullen provided concerning his police paranoia upon which the expert opinions were based.
The trial judge asked one psychiatrist, “Then why does [Cullen] endup just before he is arrested at his lawyer’s house putting himself in a passive position with his hands up against the wall if he thinks he hasn’t done anything wrong?”