The defendant appeals from conviction of armed robbery, G. L. c. 265, s. 17, and assault and battery with a dangerous weapon, G. L. c. 265, s. 1513. At trial, the defendant's sole witness was a roommate who offered an alibi for the defendant. The Commonwealth advised the judge in advance that it planned to impeach the roommate with a prior conviction of indecent assault and battery. See G. L. c. 233, s. 21. The defendant objected, arguing that the offense of indecent assault and battery was of little relevance to the roommate's credibility. In overruling the defendant's objection, the judge stated, "This is a witness, Sir, not the defendant. I don't make these kinds of discretionary calls. He's entitled to impeach if it falls within the statute and he has a certified copy."

It is a stretch to argue, as the Commonwealth does, that the judge exercised her discretion to allow use of the prior conviction. The more natural reading is that the judge ruled that her discretion to exclude such impeachment extended only to the testimony of the defendant himself, not to the testimony of other defense witnesses. The ruling was in error. The duty of the judge to exercise discretion regarding impeachment by prior convictions applies equally to the testimony of parties and of other witnesses. Commonwealth v. Buckman, 20 Mass. App. Ct. 121 , 123-124 (1985). Commonwealth v. Houston, 46 Mass. App. Ct. 378 , 381 (1999). See Commonwealth v. Burnett, 417 Mass. 740 , 743, n.1 (1994). "[I]t is the duty of the judge to exercise [discretion], and it is error as a matter of law to refuse to exercise it." Commonwealth v. Knight, 392 Mass. 192 , 194 (1984), quoting from Commonwealth v. Edgerly, 13 Mass. App. Ct. 562 , 571 (1982). See Commonwealth v. Ruiz, 22 Mass. App. Ct. 297 , 301 (1986), S.C., 400 Mass. 214 (1987).

Judgments reversed.

Karen Elizabeth Morth for the defendant.

Dean Mazzone, Assistant District Attorney, for the Commonwealth.

The defendant was convicted by a District Court jury of operating a motor vehicle while under the influence of intoxicating liquor. After the jury was discharged, the judge allowed the defendant's motion for a required finding of not guilty, pursuant to Mass.R.Crim.P. 25(b)(2), 378 Mass. 896 (1979). The Commonwealth appeals, and we reverse the judge's order.

"In deciding a rule 25 (b) (2) motion for a required finding of not guilty following a guilty verdict, . . . the judge does not properly exercise discretion concerning the weight or integrity of the evidence, but instead must assess the legal sufficiency of the evidence by the standard set out in Commonwealth v. Latimore, 378 Mass. 671 , 677 (1979). . . . Thus, the question for this court on appeal is, as it was for the judge, 'whether, after viewing the evidence in the light most favorable to the prosecution, any rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt.' " Commonwealth v. Doucette, 408 Mass. 454 , 456 (1990), quoting from Commonwealth v. Latimore, 378 Mass. at 677.

In the present case, although the evidence was not overwhelming, it was more than adequate to satisfy the Latimore standard. There was no substantial question that the defendant was operating a motor vehicle on a public way; the issue at trial concerned the defendant's alleged impairment. The Commonwealth presented testimony from the arresting officer that the defendant had veered in and out of her lane, was driving in excess of the speed limit, and, when the officer activated his lights to signal the defendant to pull over, had applied her brakes forcefully enough to leave a 37.9 foot skid mark. Additionally, the officer smelled liquor on the defendant's breath and noted that her eyes were watery and bloodshot. Her speech was slurred. When asked for her driver's license, she instead produced her credit card. The defendant also performed inadequately on all three field sobriety tests which the officer conducted. Finally, the defendant told the arresting officer that she had been out with a friend and had consumed "two mixed drinks."

This evidence, taken together, is more than sufficient to establish that the defendant's ability to operate a motor vehicle had been affected by her consumption of alcohol. See Petras v. Storm, 18 Mass. App. Ct. 330 , 334 (1984). In deciding a rule 25(b)(2) motion using the required finding standard set out in Latimore, supra, "the judge cannot weigh the evidence or assess the credibility of the witnesses. To hold otherwise would allow a trial judge to invade the province of the jury as the sole finder of fact in a jury trial." Commonwealth v. Torres, 24 Mass. App. Ct. 317 , 324 (1987).

Order allowing motion for required finding reversed.

Case remanded for sentencing on the jury verdict.

Ellyn H. Lazar-Moore, Assistant District Attorney, for the Commonwealth.

Philip T. Soloperto for the defendant.