Fighting an OUI in Massachusetts: How Cases Are Won at Trial

By Attorney Joe Serpa | Georgetown University Law Center | Massachusetts Criminal Defense Since 1995

I maintain a record of not guilty verdicts in OUI jury trials in the Massachusetts District Courts and Boston Municipal Court. I built that record since 1995 in courtrooms across Eastern Massachusetts. In this post I explain how Massachusetts OUI cases are won, from the initial stop through jury deliberations, and what the defense must do at each stage to give the defendant the best available outcome.

The trial preparation described here, and the alternatives when trial is not the right path, are covered on dismissals and not guilty verdicts.

Many of these matters can be resolved well before trial. See how criminal cases get dismissed in Massachusetts.

The Prosecution’s Burden

Under M.G.L. c. 90, § 24, the Commonwealth must prove guilt beyond a reasonable doubt, the highest standard in the legal system. An OUI conviction under § 24(1)(a)(1) requires three elements. The Commonwealth must prove that the defendant operated a motor vehicle, and that the operation occurred on a public way or in a place to which the public has a right of access. It must then prove one of two alternative theories: either that the defendant was under the influence of intoxicating liquor or drugs, or that the defendant’s blood alcohol percentage was .08 or greater.

A breathalyzer result is not proof of guilt. An officer’s opinion that the defendant seemed impaired is not proof of guilt. Each element of the offense must be established by admissible evidence, and each piece of admissible evidence is subject to challenge. The defense’s task is to identify the weakest point in the prosecution’s case and develop it fully, from the first day of representation through the jury verdict.

Layer 1: The Constitutionality of the Stop

Outside a properly conducted sobriety checkpoint, the traffic stop must have a constitutionally sufficient basis. Under the Fourth Amendment and Article 14 of the Massachusetts Declaration of Rights, an officer ordinarily must have reasonable suspicion of a motor-vehicle violation or criminal activity before initiating a stop. A stop based only on a hunch, an uncorroborated anonymous tip, or a violation the officer did not reasonably identify may be unconstitutional. See Illegal Searches and Seizures in Massachusetts and the Massachusetts Traffic Stop FAQs.

Evidence obtained from an unconstitutional stop is suppressible in its entirety through a Motion to Suppress. That includes the officer’s observations, the field sobriety test results, and the breathalyzer result. When suppression leaves the Commonwealth without admissible evidence sufficient to proceed, dismissal may follow. I have obtained dismissals at the motion stage in OUI cases involving BAC readings of .11, .13, and higher, where the stop that led to those readings was constitutionally defective.

The full stop framework, updated for Commonwealth v. Arias, SJC-13816 (Mass. Apr. 15, 2026), which suppressed a stop made a day after the observed infraction, is at Massachusetts Traffic Stops, Exit Orders, and Pretext Searches. The role of phones, GPS records, and license plate readers is covered in The Modern Massachusetts Traffic Stop.

The firm’s companion article on cross-examining the field sobriety opinion explains that part of the trial in detail.

Dash camera footage, body camera footage, and the officer’s written report are the primary sources for a suppression motion. They are demanded in every case before any motion deadline passes.

Layer 2: The Field Sobriety Tests

An officer may direct a driver to perform roadside field sobriety tests when specific and articulable facts create reasonable suspicion of OUI. The officer need not obtain consent or advise the driver of a right to refuse the exercises. Police may not use physical force to compel performance. Declining the exercises causes no automatic Registry suspension, and evidence that the driver declined the exercises is generally inadmissible at trial. A judge may permit narrow rebuttal if the defense creates a misleading impression of complete cooperation or suggests that no exercises were offered.

When officers administer the standardized field sobriety tests, they should follow the National Highway Traffic Safety Administration instructions for the horizontal gaze nystagmus, walk and turn, and one leg stand. NHTSA warns that changes may compromise the validity of the exercises. A material departure can support an admissibility challenge when the governing foundation requires it, and departures provide focused cross-examination. Not every departure automatically excludes the evidence. Body-camera and dashboard-camera footage often provides the best comparison between the officer’s scoring and the driver’s actual performance.

The Supreme Judicial Court also limits how this evidence comes before a jury. In Commonwealth v. Gerhardt, 477 Mass. 775 (2017), the court held that in marijuana OUI cases these roadside exercises must be described as roadside assessments rather than as scientific tests. The officer may describe the driver’s balance, coordination, and mental acuity, but may not testify that the driver passed or failed, and no witness who is not a qualified expert may offer an opinion that a driver was under the influence of marijuana.

The court also required a jury instruction that performance on roadside assessments, standing alone, is never enough to convict in a marijuana case.

Non-alcohol-related causes of HGN nystagmus, inner ear conditions, and fatigue are available as cross-examination material when the officer relies heavily on the HGN test. The OLS and WAT results are similarly subject to challenge when the testing surface was uneven, when the defendant was wearing heels, or when the pre-test instructions were not given correctly. See Massachusetts OUI Defense.

Layer 3: The Breathalyzer

The Draeger Alcotest 9510 is the evidentiary breath-test instrument used in Massachusetts under 501 CMR 2.00. A reported result of .08 or greater can support the alcohol-percentage theory under M.G.L. c. 90, § 24, but the number does not establish guilt by itself. The Commonwealth must establish operation, the covered location, the applicable time and alcohol percentage, and the admissibility and reliability of the result. I examine each of those issues rather than treating the reported number as the end of the case.

The 15-minute observation period. Before administering the Alcotest, the breath-test operator must observe the defendant for at least 15 minutes under 501 CMR 2.13. If the operator has reason to believe that the defendant brought a substance into the mouth, the operator must restart the observation period. The report, booking-room video, and testimony can support a challenge to the Commonwealth’s foundation. A momentary look away or every possible mouth event does not automatically require suppression; the actual deviation, foundation, and prejudice must be evaluated in the particular case.

Calibration and maintenance records. The consolidated Commonwealth v. Ananias litigation exposed the Office of Alcohol Testing’s withholding of hundreds of failed calibration worksheets. In Commonwealth v. Hallinan, 491 Mass. 730 (2023), the Supreme Judicial Court held that a defendant whose evidence included a result from an Alcotest 9510 device last calibrated and certified before April 18, 2019 receives a conclusive presumption of egregious government misconduct. An affected result must be excluded in any pending or future prosecution. For postconviction relief, however, Hallinan does not create a conclusive presumption of prejudice.

The Hallinan Checklist for Clients and Lawyers

• Obtain the breath-test ticket and identify the device model and serial number.
• Obtain the device history and determine when the Alcotest 9510 was last calibrated and certified.
• Confirm whether the device was last calibrated and certified before April 18, 2019.
• Confirm that the result formed part of the evidence against the defendant.
• Identify whether the case is pending or ended in a guilty plea, an admission to sufficient facts, or a conviction after trial. For a completed case, collect the docket, plea or trial record, discovery, and sentence before evaluating a Rule 30 motion.

A defendant who pleaded guilty or admitted to sufficient facts must show a reasonable probability that the defendant would have rejected the disposition and proceeded to trial if the misconduct had been known. A defendant convicted after trial must file a Rule 30 motion and establish a legally sufficient basis for a new trial. For any result not excluded under Hallinan, I examine the calibration, certification, maintenance, and discovery records for the particular instrument and result.

The ±0.020 internal-consistency requirement. 501 CMR 2.14 requires a sequence consisting of one adequate breath sample, one control-standard analysis, and a second adequate breath sample. The two breath samples must be within ±0.020 blood alcohol content units. When they are not, the sequence is invalid and a new sequence must begin. The two readings appear in the breath-test record and are reviewed in every case.

Medical conditions. Gastroesophageal reflux disease, acid reflux, diabetes, and medication do not automatically invalidate a breath-test result. A documented condition may support a case-specific challenge when medical records and qualified expert testimony establish a reliable connection to mouth alcohol, acetone, or another relevant analytical issue. I review the actual diagnosis, symptoms, treatment, timing, test record, and available video before deciding whether the condition belongs in the defense.

The rising alcohol-percentage issue. A breath test occurs after the alleged operation, and a later result may not establish the alcohol percentage at the time of driving. Whether the defendant’s alcohol percentage was still rising depends on the drinking pattern, food, elapsed time, physiology, and other case-specific facts. The timing of the last drink, quantity consumed, body weight, arrest, and breath test can support the analysis, and qualified expert testimony may be necessary.

The right to an independent examination. A person held on an OUI charge has a statutory right under M.G.L. c. 263, § 5A to an immediate examination, at the person’s own expense, by a physician of the person’s choosing. Police must inform the defendant of that right and provide a reasonable opportunity to exercise it. If police deny or materially frustrate the opportunity, the judge determines the appropriate remedy from the circumstances and resulting prejudice. Dismissal is not automatic in every case.

A defendant who refused the breathalyzer faces a different evidentiary and licensing analysis. Evidence that the defendant refused the breath test is generally inadmissible in the criminal prosecution under M.G.L. c. 90, § 24(1)(e) and Article 12 of the Massachusetts Declaration of Rights. The protection is not absolute after the defense opens the door. If the defense creates a misleading impression of complete cooperation or suggests that police never offered the breath test, the judge may permit narrow evidence that the defendant refused the breath test in rebuttal. Statements or conduct during an attempted test require separate analysis.

Layer 4: The Trial

When motions are denied and the case proceeds to trial, the defense continues. An OUI jury trial in Massachusetts District Court is typically a one-day proceeding. The jury is composed of six jurors under M.G.L. c. 218, § 26A. The defense cross-examines the arresting officer and any other prosecution witnesses, moves to exclude specific pieces of evidence, and presents its own witnesses and exhibits.

Massachusetts law limits what the arresting officer may tell that jury. Under Commonwealth v. Canty, 466 Mass. 535 (2013), an officer may offer a lay opinion about the defendant’s apparent level of sobriety or intoxication, but may not opine that the defendant operated under the influence or that alcohol diminished the defendant’s ability to drive safely. Those ultimate questions belong to the jury alone, and effective cross-examination holds the officer to that line.

The most effective OUI trial defense presents the jury with a complete factual picture that the prosecution’s evidence does not capture. Booking room video showing the defendant speaking clearly, walking without difficulty, following instructions, and appearing coherent can contradict the officer’s characterization of the defendant as impaired. Dash camera footage showing controlled, lawful driving before the stop can contradict the impairment theory. Witness testimony from passengers or bystanders who observed the defendant before and during the stop is available when it exists.

Expert testimony may assist the jury when a breath-test, rising-alcohol-percentage, or pharmacology issue is supported by the evidence. I prepare cross-examination of the officer from the case-specific record, including the field-sobriety instructions and scoring, observation-period evidence, and breath-test procedures.

I have tried OUI cases in which the defendant had a BAC reading of .11, .13, and higher and secured not-guilty verdicts. The BAC number is the beginning of the analysis, not the end. A representative sample of trial results is available at Massachusetts Criminal Defense Trial Results.

OUI Trial Results: A Recent Representative Sample, 2025-26

• OUI Third Offense, Woburn District Court. Not guilty all counts.
• OUI, Concord District Court. Not guilty all counts.
• OUI, Third Offense, Lawrence District Court. Not guilty all counts.
• OUI, Second Offense, Waltham District Court. Not guilty all counts.

For the complete list of trial results including Superior Court felony acquittals, see Massachusetts Criminal Defense Trial Results. Local guides to how OUI cases move through two of the busiest courts in the region are available at Woburn District Court OUI and Criminal Cases and Quincy District Court Criminal Cases.

When to Go to Trial and When Not To

Not every OUI case is a trial case. Cases with a constitutionally defective stop are resolved through a Motion to Suppress and dismissal. Cases with borderline BAC, favorable video, and a credible sobriety narrative are strong trial candidates. Cases with strong evidence of impairment, a high BAC, and no constitutional infirmity may be better resolved through negotiation for the best available disposition.

I make the decision to go to trial with the defendant after reviewing all available evidence. The decision is never based on the reported alcohol number alone. For an eligible defendant, Section 24D is itself the probationary or sentencing disposition. It may take the form of a continuance without a finding after an admission to sufficient facts, or it may be the sentence imposed after a guilty plea or a conviction at trial. The disposition includes probation for no more than two years, assignment to the required program, and a 45-to-90-day license suspension, or 210 days if the person was under 21 at the time of the offense.

Professional licensing, immigration, commercial-driving, federal-employment, and other consequences are record-specific. In some cases, those consequences make dismissal or a not-guilty verdict the client’s only acceptable objective. See Massachusetts OUI FAQs.

Key Takeaways

• The prosecution must prove every element of an OUI charge, operation, a public way, and impairment or a .08 BAC, beyond a reasonable doubt. A breathalyzer reading does not establish guilt.
• An unconstitutional traffic stop renders all resulting evidence suppressible through a Motion to Suppress. See Illegal Searches and Seizures in Massachusetts.
• Police may direct field sobriety tests when reasonable suspicion supports the request, but police may not compel performance by physical force. Refusing the exercises causes no automatic Registry suspension, and evidence that the driver refused the exercises is generally inadmissible, subject to narrow rebuttal if the defense opens the door. NHTSA departures may affect admissibility or weight and provide cross-examination; they do not all require automatic exclusion.
• A reported Alcotest 9510 result may be challenged through the observation-period evidence, calibration and certification records, test sequence, medical evidence, timing, and other case-specific proof. A regulatory issue does not automatically require exclusion, and a medical condition does not invalidate a result without a supported connection to the test.
• Booking room video, dash camera footage, and witness testimony can directly contradict the prosecution’s impairment narrative at trial.
• A continuance without a finding is not a conviction under Massachusetts criminal law, but it can remain important for later OUI counting, immigration analysis, professional licensing, commercial driving, and other collateral matters. The consequence depends on the governing law and the person’s record.

When the breath or blood number decides the case, the science set out on the firm’s breath test and blood alcohol science page provides the cross-examination.

I represent defendants in OUI cases across the Massachusetts District Courts and Boston Municipal Court. I am a Georgetown Law graduate, have practiced Massachusetts criminal defense since 1995, and have a record of not-guilty verdicts in OUI jury trials. Contact me at 617.936.0201 for a free consultation. My Boston office is at 20 Park Plaza #400A, and my Quincy Office is at 500 Victory Road, Suite 400A.

Related Resources

• OUI Defense in Massachusetts, Main Practice Area Page
• Massachusetts OUI FAQs
• Massachusetts OUI License Suspensions
• Should I Take the Breathalyzer in Massachusetts?
• Breathalyzer Defense in Massachusetts
• What Happens After an OUI Arrest in Massachusetts
• Illegal Searches and Seizures in Massachusetts
• CWOF, Pretrial Probation, and Diversion in Massachusetts FAQs
• Criminal Defense for Licensed Professionals in Massachusetts
• Massachusetts Criminal Defense Trial Results
• Boston Municipal Court
• Quincy District Court
• Cambridge District Court
• Dedham District Court
• Woburn District Court
• Waltham District Court