Our task in circumstances such as the present is to ascertain "whether there is a substantial risk of a miscarriage of justice." Commonwealth v. Freeman, 352 Mass. 556 , 564 (1967). Contrast Commonwealth v. O'Brien, 377 Mass. 772 , 778-779 (1979), and cases cited. We believe that the prosecutor's closing argument, when viewed in its totality, exceeded the bounds of permissible argument. See Commonwealth v. Burke, 373 Mass. 569 , 577 (1977), and cases cited. See also Commonwealth v. Montecalvo, 367 Mass. 46 , 56 (1975).
The prosecutor's closing argument indicated that he had personal knowledge independent of the trial evidence (e.g., "believe me, no one in Chelsea is selling [heroin] half-price to anybody"). See S.J.C. Rule 3:22A, PF 14, 377 Mass. 927 (1979) (effective March 1, 1979). Contrast Commonwealth v. Hogan, 375 Mass. 406 , 407-408 (1978). There were several instances, among the many improprieties, where the prosecutor's remarks could be read as expressing a personal opinion of the defendant's guilt (e.g., "I would guess that he supplements his income with the sale of heroin"). See United States v. Gonzalez Vargas, 558 F.2d 631, 632 (1st Cir. 1977). Compare Commonwealth v. Coleman, 366 Mass. 705 , 713-714 (1975). Contrast United States v. Cotter, 425 F.2d 450, 452-453 (1st Cir. 1970). It is also apparent from the prosecutor's argument that he was vouching for the credibility of the Commonwealth's witnesses (e.g., "believe me, these police officers know full well what's going on here"), as well as expressing a personal disbelief in the credibility of the defendant (e.g., "If he could not . . ., then I'm mistaken"). See Commonwealth v. DeChristoforo, 360 Mass. 531 , 546-547 & n.4 (1971), and cases cited (Tauro, C.J., dissenting). Contrast Commonwealth v. Stone, 366 Mass. 506 , 516 (1974). As the defendant's defense depended heavily upon the jury's assessment of his credibility, these remarks unfairly undercut the very heart of his defense. See Commonwealth v. Shelley, 374 Mass. 466 , 470-471 (1978). Contrast Commonwealth v. St. Pierre, 377 Mass. 650 , 655 (1979). And, by commenting on and suggesting that inferences be drawn from matters not in evidence, the prosecutor injected into the juror's minds impermissible and unnecessarily prejudicial factors (e.g., that the police had prior knowledge of defendant's involvement in drug transactions). See Commonwealth v. Shelley, supra at 470. Also, there were several references to the corroborative effect of the putative testimony of a police officer who did not testify. Thus, when the totality of various and frequent (at least ten) improper remarks (e.g., "believe me, that's not so") in the closing argument are viewed in conjunction with the judge's failure to utter a critical instruction that closing argument is not evidence (see Commonwealth v. DeChristoforo, supra at 549 [Tauro, C.J., dissenting]; contrast Donnelly v. DeChristoforo, 416 U.S. 637, 644  [same case]; Commonwealth v. St. Pierre, supra; Commonwealth
v. O'Brien, supra at 777), we are constrained to conclude that "there is a substantial risk of a miscarriage of justice" (Commonwealth v. Freeman, supra) and that the defendant must have a new trial. See Donnelly v. DeChristoforo, 416 U.S. at 648 n.23.
In reaching the result we are mindful that recently the Chief Justice of the Supreme Judicial Court carefully reiterated the oft-stated, but infrequently followed, guidelines for closing argument. Commonwealth v. Earltop, 372 Mass. 199 , 205-206 (1977) (Hennessey, C.J., concurring). See also DeChristoforo v. Donnelly, 473 F.2d 1236, 1238 & n.3 (1st Cir. 1973), rev'd, 416 U.S. 637 (1974) (but see id. at 648 n.23). For an extensive, but not exhaustive, list of exemplary cases on this point, see Commonwealth v. Earltop, supra at 205 n.1. In addition, we canvassed the many cases collected in Commonwealth v. Edgerly, 6 Mass. App. Ct. 241 , 260 (1978). We think the present case is more nearly like Commonwealth v. Burke, supra, Commonwealth v. Shelley, supra, and Commonwealth v. Redmond, 370 Mass. 591 (1976), than the other cases cited therein (see e.g., Commonwealth v. Nordstrom, 364 Mass. 310 , 313-316 ), and thus should be treated accordingly. Contrast Commonwealth v. Fitzgerald, 376 Mass. 402 , 416-424 (1978); Commonwealth v. Dougan, 377 Mass. 303 , 312 (1979); Commonwealth v. St. Pierre, supra; Commonwealth v. O'Brien, supra at 778 ("It is long past time for prosecutors to prepare their closing arguments carefully in order to avoid the possibility of reversals of convictions because of prosecutorial error").
Verdict set aside.