The defendant was convicted and sentenced on two indictments charging the distribution of a controlled substance (heroin) (G. L. c. 94C, Section 32) and has appealed. He assigns as error the exclusion of questions designed to impeach the credibility of a prosecution witness, a special agent in the United States Department of Justice Drug Enforcement Administration. The purpose of the questions was to bring out that in an unrelated drug case the witness had engaged in what the defendant claims was improper conduct. The concluding question of the series was, "Involving any of your cases, has there been any investigation made of you?" In ruling on the prosecutor's objection, the judge said, "Sustained. It's a highly irregular question . . . . Most improper." We agree with the judge's characterization. Despite rules to the contrary in other jurisdictions, "[i]n Massachusetts, the rule has been that a witness cannot be asked on cross-examination, in order to affect his credibility, about his part in transactions irrelevant to the issue on trial." Commonwealth v. Schaffner, 146 Mass. 512 , 515 (1888). Commonwealth v. Turner, 371 Mass. 803 , 809-810 (1977). See Leach & Liacos, Massachusetts Evidence 122-123 (4th ed. 1967); Hughes, Evidence Section 238, at 279 (1961). The
evidence was inadmissible for another reason. The defendant relies on memoranda of two judges of the United States District Court, District of Massachusetts, to support his conclusion that there had been prior misconduct by the witness. Read in their entirety, these memoranda do not support this conclusion, and thus the questions were properly excluded apart from any violation of the above rule. See Commonwealth v. Homer, 235 Mass. 526 , 535-536 (1920).
The cases of Commonwealth v. Franklin, 366 Mass. 284 (1974), and Commonwealth v. Bohannon, 376 Mass. 90 (1978), are distinguishable on their facts and do not aid the defendant.