1. The defendant's motion for a new trial was addressed to the sound discretion of the trial judge, Commonwealth v. Gange, 367 Mass. 519 , 526 (1975). and cases cited, whose denial thereof was not an abuse of discretion. Indeed, we find no plausible reason why he might have chosen to exercise his discretion the other way. 2. The supplementary charge to the jury closely and correctly followed the language of Commonwealth v. Tuey, 8 Cush. 1 , 2-3 (1851), as modified by Commonwealth v. Rodriquez, 364 Mass. 87 , 97-98 (1973). 3. The contention that the defendant was denied the effective assistance of counsel is without merit. An examination of the transcript demonstrates that trial counsel for the defendant represented him with ability and effectiveness at every stage of the trial. Counsel's inability to get the witness Desrochers to acknowledge that he had told the defendant that he, Desrochers, had perpetrated the crimes with which the defendant was charged was not for want of trying; it is quite clear from the transcript that Desrochers was unwilling to volunteer any such testimony, particularly after the judge properly advised him of his right to refuse to give testimony incriminating himself. The defendant's further contentions that counsel discouraged him from taking a lie detector test and from taking the stand in his own defense, even if credited, do not suggest to us that counsel was acting other than prudently and in the best interests of the defendant. Judgments affirmed.

The defendant appeals pursuant to G. L. c. 278, Sections 33A-33G, from his conviction for possession of a controlled substance (heroin) with intent to

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distribute. 1. The defendant's pretrial motion for disclosure of the identities of the informants upon whom the police relied in applying for the search warrant was properly denied by the judge. See Roviaro v. United States, 353 U.S. 53, 59 (1957). The informants did not testify against the defendant (compare Smith v. Illinois, 390 U.S. 129 [1968]), and the informants were not witnesses to the actual criminal activity with which the defendant was charged (compare Commonwealth v. Johnson, 365 Mass. 534 [1974]). Nor has the defendant indicated that the informants' testimony might, in any manner, be relevant to his case. See McCray v. Illinois, 386 U.S. 300, 311-313 (1967); Commonwealth v. Mott, 2 Mass. App. Ct. 47 , 53 (1974). Compare Commonwealth v. Ennis, 1 Mass. App. Ct. 499 , 501-503 (1973), and cases cited therein. 2. The defendant's contention that the search of his property was carried out with unreasonable force so as to taint the entire search and make any evidence seized excludable is without merit. The doctrine of trespass ab initio has no application to these circumstances. McGuire v. United States, 273 U.S. 95, 99 (1927). But cf. Ker v. California, 374 U.S. 23, 33-34 (1963). 3. Nor was there error in the exclusion at trial of photographs purportedly depicting the store after the search as these photographs were not material to any issue before the jury. 4. The defendant asserts that the Commonwealth failed "to fully and truthfully respond" to his pretrial discovery motion. Assuming without deciding that the defendant's motion called for the production of his oral admission (contrast Commonwealth v. Nichols, 4 Mass. App. Ct. 606 , 608, n.1 [1976]), the defendant has not demonstrated that the Commonwealth's alleged failure was prejudicial (Commonwealth v. Dabrieo, 370 Mass. 728 , 744 [1976]), or "of sufficient significance to result in the denial of . . . [his] right to a fair trial." United States v. Agurs, 427 U.S. 96, 108 (1976). See Commonwealth v. Nichols, supra, at 612, n.6. Compare Moore v. Illinois, 408 U.S. 786, 794-795 (1972). 5. The defendant was given the Miranda warnings in English and Spanish. The judge's determination that the Commonwealth had met its heavy burden of demonstrating that the defendant understood his rights and knowingly waived them is supported by the evidence. Commonwealth v. Roy, 2 Mass. App. Ct. 14 , 18 (1974). Commonwealth v. Haglund, 4 Mass. App. Ct. 858 , 859 (1976). 6. No error was committed by the judge in permitting the introduction in evidence of certificates of analysis prepared by an assistant analyst of the Department of Public Health to establish that the substance in question was heroin. The Department of Public Health is authorized by statute to make this kind of analysis (G. L. c. 111, Section 12), and the certificates were admissible under G. L. c. 111, Section 13. Commonwealth v. Harvard, 356 Mass. 452 , 461-463 (1969). Commonwealth v. Baribeault, 2 Mass. App. Ct. 839 (1974). 7. The judge properly denied the defendant's motion for a directed verdict. There was ample circumstantial evidence from which the jury could have concluded that the defendant had knowledge of the heroin and possessed it with intent to distribute it. Commonwealth v. Nichols, supra, at 613-614, and cases cited therein. 8. The defendant has waived all other assignments of error.

Judgment affirmed.