Convicted of unlawfully carrying a firearm, unlawful possession of ammunition, and unlawful possession of cocaine, the defendant, Angel Paniaqua, appeals.1 On appeal, the defendant claims error in (1) the denial of his motion to suppress; (2) the Commonwealth’s exercise of a peremptory challenge; and (3) the denial of his motions for required finding because the evidence was insufficient to support the convictions. We affirm.
1. The motion to suppress.2 At issue is whether exigent circumstances justified the police officers’ warrantless entry into an apartment where the defendant was arrested and the seizure of items in plain view. There was testimony from which the judge could find that Boston police Officer William E. Doogan, while patrolling in a police vehicle, received a radio report that gunshots had been fired in a hallway at 166 Seaver Street in the Roxbury section of Boston. Doogan arrived at that location in about one minute. Within another minute or two, several other officers arrived, and all of the *798officers went into the building. On the second floor, a woman in the hallway said, “[T]hey ran in there,” as she pointed to the rear door of a third-floor apartment. Three officers went up the front stairway, and two ascended the rear stairway, to the third floor. Some of the officers had drawn their guns. As the two officers ascended the rear stairs, a man later identified as Eduardo Diaz opened the rear door of the third-floor apartment, looked out, and then closed the door. Diaz then opened the apartment’s front door and asked the officers there what they wanted. Diaz told the officers that he knew nothing about a shooting. The officers stepped inside. Doogan entered the apartment and saw the defendant running toward the kitchen while carrying a gun. Doogan and another officer chased the defendant. The defendant threw the gun and a tinfoil ball into a trash can. An officer retrieved the gun, which was loaded, and the foil ball. We believe that the judge was warranted in concluding that the circumstances known to the officers created an exigency which, along with probable cause, justified the warrantless entry.
A police radio call alerted the police to a probable firing of shots at 166 Seaver Street. The police reasonably believed the circumstances to be life-threatening. The rapid response by five officers within three minutes of the radio report meant that there was a strong possibility that the person who fired the shots still was at 166 Seaver Street. The woman in the second-floor hallway identified the third-floor apartment occupied by the defendant as the location of the person who fired the shots. The opening and closing of the rear door to that apartment further identified that apartment as a possible location of a suspect. The facts here clearly warranted the officers to conclude that there was a danger to the public and that at least one suspect and one weapon would be located at 166 Seaver Street. Speed would be essential if the person who fired shots were to be apprehended. The judge correctly concluded that the Commonwealth had sustained its burden of proving that exigent circumstances and probable cause justifying the police officers’ entry into the apartment existed. See Commonwealth v. Franklin, 376 Mass. *799885, 899-900 (1978). The subsequent seizure of the firearm, ammunition, and foil ball was lawful. There was no error in denying the defendant’s motion to suppress.
2. The Commonwealth’s use of a peremptory challenge.' The defendant asserts that he is entitled to a new trial because the judge erred in requiring the defendant to choose between a stay of the trial pending an appeal or to proceed to trial without a juror who was peremptorily challenged by the Commonwealth. In the course of jury empanelment, the prosecutor challenged one juror. Defense counsel objected, stating, “He’s obviously Hispanic. The Defendant is Hispanic.” The judge disallowed the challenge. The prosecutor responded that, “under [Commonwealth v. Soares, 377 Mass. 461, cert, denied, 444 U.S. 881 (1979)] there has to be a pattern.” The judge then asked the prosecutor why she was challenging the juror. She answered, “I’m challenging him, first of all, because I don’t like his looks. Secondly, he lives in Hawthorne Place’ He’s young; he’s single. And he’s watching me in a strange manner.” The judge again rejected the challenge, suggesting that she could seek relief from a single justice of this court.
On the following Monday, the prosecutor moved for reconsideration of the disallowance of the peremptory challenge on the ground that there had been no showing of a pattern of excluding Hispanic jurors. The judge denied the motion. The Commonwealth then sought relief from a single justice of this court. The single justice conducted a hearing on the “Commonwealth’s Application Pursuant to G. L. c. 211, Sec. 3 For Leave To Appeal The Denial of a Peremptory Challenge During Empanelment.” After hearing counsel, the single justice announced that he would reserve and report the matter to the full court unless the parties could “work it out [them] selves.”
The proceedings then resumed in the trial court. The judge said that since there were “only two individuals of Hispanic origin in the . . . group of potential jurors . . . out of fifty, the Defendant’s objection to the peremptory challenge exercised by the Commonwealth was deemed by [the judge] to be mer*800itorious.” “Moreover,” he said, “the reasons stated by the Assistant District Attorney bordered on the ludicrous. This Court determined that it would not permit the exercise of such a peremptory challenge. There is a pattern of exclusion of a distinct ethnic group when, out of two people summonsed to the courtroom, one is challenged from the jury for no reason whatsoever. Accordingly, and in order to comply with the wishes of the Supreme Judicial Court, these proceedings are stayed.”
Defense counsel objected, stating that, if the trial were to be stayed until the juror issue was resolved in the Supreme Judicial Court, the trial would not take place for another six months, during which time the defendant would be required to remain in jail. Thus, said counsel, “We would be prepared to work out whatever accommodation, including impanelling a new jury tomorrow . . . .” The judge replied that, rather than empanelling a new jury, a juror could be seated to replace the challenged juror. Defense counsel said, “Whatever the accommodation is, we are not able to withstand a six month delay. And we are prepared to go ahead.” Counsel also announced that he was not giving up his right to appeal the question whether the defendant was entitled to have the challenged juror on his jury, but, if his only choice was to wait six months for the juror issue to be resolved by the Supreme Judicial Court or to go ahead with the trial, he would go ahead with the trial.
The defendant now argues that his choice to proceed with the trial, without the challenged Hispanic juror, rather than delay the trial for a six-month period during which the defendant would remain in jail, cannot fairly be deemed to be a voluntary relinquishment of his right to argue on appeal that the challenged juror was excused erroneously. We recognize that the defendant may have been put to a difficult choice; however, we are not persuaded that it is unfair to hold the defendant to his choice to proceed without the juror, knowing all the circumstances. The defendant made his choice and cannot now claim error by the judge.
*8013. The sufficiency of the evidence. “ ‘In reviewing the denial of a motion for a directed verdict in a criminal case, [the court determines] whether the evidence offered by the Commonwealth, together with reasonable inferences therefrom, when viewed in its light most favorable to the Commonwealth, was sufficient to persuade a rational jury beyond a reasonable doubt of the existence of every element of the crime charged.’ Commonwealth v. Campbell, 378 Mass. 680, 686 (1979). See Commonwealth v. Latimore, 378 Mass. 671, 676-677 (1979); Jackson v. Virginia, 443 U.S. 307, 318-319 (1979).” Commonwealth v. Stewart, 398 Mass. 535, 540 (1986). “It is sufficient that the evidence permitted the inference which the jury obviously drew against [Paniaqua].” Commonwealth v. Nelson, 370 Mass. 192, 203 (1976).
Possession is the intentional exercise of control over an item. Commonwealth v. Brzezinski, 405 Mass. 401, 409 (1989). There was ample evidence at the trial that the defendant possessed a gun containing ammunition. He threw the loaded gun into a trash can. At issue is the conviction for unlawful possession of cocaine.3
The evidence concerning the foil ball, in the light most favorable to the Commonwealth, may be summarized as follows. The defendant threw a foil ball into the trash can. The contents of the foil ball were described as “a white rock-like and powdery substance [which the officer] believed ... to be cocaine.” The certificate issued by the Commonwealth pursuant to G. L. c. Ill, § 13 (1990 ed.), certifies that the “powder contained in 3 aluminum foil” packets was examined (emphasis supplied). “The powder was found to contain: Cocaine.” The analysis indicates that there was 10.43 grams of cocaine. The jury therefore could have determined that at least one, if not all three, of the foil packets contained powder which was determined to be cocaine.4
*802The jurors knew that the foil ball contained a white powdery substance which the officers believed to be cocaine. The jurors could credit the officers’ beliefs that the white powdery substance was cocaine. Officer Stevens, for example, testified in response to a question by the defense that he (Stevens) would not “testify about something that he was not certain about.” (At the time of trial, Stevens had been on hundreds of drug raids.) Another officer stated, in response to a question by the defense, that this was not the first arrest he had made where drugs were found. The defendant did not challenge the expertise of the officers at trial.5 Further, throughout the trial, both the Commonwealth and the defendant repeatedly asked questions as to what substances were found and what the officers saw. The opinion of one of the officers was elicited by the defendant on cross-examination. The defendant did not raise any objection to the officers’ expertise as to what contraband (drugs) was observed in the apartment that night. Throughout the trial, the defense strategy was to challenge the Commonwealth’s claim that the defendant possessed the items (the gun, the bullet, and the drugs) and the chemical analysis. At no time has the defendant challenged the expertise of the officers. “The theory of law *803on which by assent a case is tried cannot be disregarded when the case comes before an appellate court for review. . . .” Commonwealth v. Fernette, 398 Mass. 658, 667 (1986), quoting Santa Maria v. Trotto, 297 Mass. 442, 447 (1937).6
“Absent objection, the hearsay evidence was properly admitted, and the jurors were entitled to give it such probative effect as they deemed appropriate.” Abraham v. Woburn, 383 Mass. 724, 726 n.l (1981). See Commonwealth v. Keevan, 400 Mass. 557, 562 (1987). Accord People v. Bailey, 1 Cal. App. 4th 459 (1991). Additionally, there was evidence that (in addition to running away from the police and throwing the foil bag into the trash can) the defendant gave a false name and changed his appearance by the time of trial. There was, therefore, extensive evidence of the defendant’s consciousness of guilt. See Commonwealth v. Doucette, 408 Mass. 454, 461 (1990) (“Actions . . . that indicate a defendant’s consciousness of guilt together with other evidence are sufficient to prove . . . guilt”).7
Judgment affirmed.
The judge sentenced the defendant on the firearm charge and placed the other two convictions on file. “However, since the placing of a case on file does, inter alia, suspend, for as long as the case remains on file, a defendant’s right to appeal alleged error in the proceeding, the defendant must consent to the filing” (emphasis supplied). Commonwealth v. Delgado, 367 Mass. 432, 438 (1975). Commonwealth v. Mora, 402 Mass. 262, 263 n.l (1988). The better practice is not to place a case on file without the defendant’s consent. Because the record does not reflect the defendant’s consent to two convictions’ being placed on file we shall consider them.
The judge did not make any findings of fact. Failure to make findings is not fatal, however, when the record makes the judge’s reasoning clear. See Commonwealth v. Parham, 390 Mass. 833, 837-838 (1984); Commonwealth v. Forrester, 365 Mass. 37, 44-45 (1974); Commonwealth v. Ayles, 31 Mass. App. Ct. 514, 517 (1991). It is clear from the judge’s discussion with counsel that the judge’s denial of the defendant’s motion to suppress was grounded on the judge’s determination that the officers’ entry into the third-floor apartment was dictated by both exigent circumstances and probable cause as disclosed by the testimony of two of the participating officers.
The defendant was charged with trafficking in cocaine. The judge reduced the trafficking charge to possession of cocaine.
Indeed, in his closing argument, defense counsel conceded that the jury might draw such an inference. He said: “We know that somebody’s [foil package] had cocaine in it, because we have three packets in there; and *802the laboratory said there’s cocaine. There isn’t any clear indication that what [the defendant] had had dope in it. However, I would submit that if they found two packets with tinfoil, and there’s another packet that he had that looks like it, maybe you can conclude that his packet had dope in it, if you believe . . . that [the defendant] was dumb enough to stand there with a tinfoil packet and wait until the police came in; and, then, when they came in, in their presence throw it in the trash. I submit to you that part of it is totally incredible.”
Indeed, even on appeal, the defendant has not argued that the oEcers were not qualified to express their opinion on the nature of the substance. “[W]e may consider issues on appeal not raised at trial [or, in this case, even on appeal], but our power to do so is rarely exercised, and is exercised only in response to a serious and obvious error creating a substantial risk of a miscarriage of justice.” Commonwealth v. Pares-Ramirez, 400 Mass. 604, 609 (1987). This conviction does not meet that standard especially in light of the fact no judgment has been imposed on this offense. The defendant has not complained or sought to have himself discharged or sentenced on this conviction. See Commonwealth v. Delgado, 367 Mass. 432, 438 (1975).
Clearly, it would have been better for the Commonwealth’s trial counsel to make explicit the drug training and experience of the officers. The defendant himself brought out much of the evidence of the officers’ opinion and expertise. Appellate counsel for the Commonwealth was not trial counsel.
Evidence of consciousness of guilt alone cannot support a conviction but “evidence of such a state of mind when coupled with other probable inferences, may be sufficient to amass the quantum of proof necessary to prove guilt.” Commonwealth v. Booker, 386 Mass. 466, 470 (1982), citing Commonwealth v. Best, 381 Mass. 472, 483 (1980); Commonwealth v. Porter, 384 Mass. 647, 653 (1981). Here, the observation of the white powder, the officer’s familiarity with drug control, and the laboratory report that the white powder was cocaine provide that additional evidence.