NOT GUILTY: OUI Second Offense Acquittal Despite .09 Breath Test

How understanding breath test deviation led to a Judgement of not guilty

June 12, 2026 | OUI Defense | Attorney Michael P. Murray

Today, my client was found NOT GUILTY in Commonwealth v. [Defendant], Docket No. 2567 CR 1397. My client had been charged with Operating Under the Influence of Alcohol—Second Offense—after recording a breath test of .09.

A second-offense OUI conviction in Massachusetts carries severe mandatory penalties: a two-year loss of license, a mandatory minimum of two years probation, and a 14-day inpatient program at a state facility—which in practice means 60 days in the House of Correction.

My client left court today with his license reinstated and no sentence at all.

Here’s how we won.

The Traffic Stop: A Hands-Free Violation

My client was stopped for a hands-free violation—using his cell phone while driving. There was no erratic driving, no accident, no swerving between lanes. Just a cell phone.

After the stop, the officer conducted field sobriety tests and ultimately administered a breath test. The result: .09—one hundredth of a percentage point above the legal limit of .08.

For most people, a .09 breath test feels like the end of the road. It’s above the limit. The machine said so. Case closed.

But that’s not how the science works.

The Science: What the Breath Test Actually Measures

At trial, the arresting officer testified honestly about two critical facts that many people do not understand:

First: Breath test machines have an acceptable standard deviation of ± .02.

This means that even a properly calibrated, properly functioning breath test machine can produce a result that is off by as much as .02 in either direction. A reading of .09 could actually represent a true blood alcohol content anywhere from .07 to .11. A .09 reading could mean my client was below the legal limit.

Second: The breath test machine does not measure blood alcohol content—it estimates it.

The machine takes a sample of breath, not blood. It then runs that breath sample through a complex mathematical computation to estimate what the person’s blood alcohol content might be. This estimation process introduces another layer of potential deviation.

When you combine the machine’s inherent margin of error with the uncertainty introduced by the breath-to-blood estimation, a .09 reading is far from conclusive proof that someone was above the legal limit.

The Judgement: Reasonable Doubt

The Commonwealth must prove guilt beyond a reasonable doubt. When the machine itself has a margin of error that could place the defendant below the legal limit, and when the machine is estimating blood alcohol from breath rather than measuring it directly, reasonable doubt exists.

The court understood this.

A Note on Professionalism

I want to acknowledge something that made this verdict possible: the honesty of the arresting officer.

When asked about the breath test machine’s margin of error, the officer testified truthfully. When asked whether the machine measures blood or estimates it from breath, the officer explained the science accurately. The officer did not shade the truth, did not evade, did not advocate.

I am never surprised, but I remain impressed and grateful for the honesty, integrity, and professionalism shown by law enforcement professionals in Massachusetts. They consistently testify under oath and speak the truth without reservation—even when the truth might be inconsistent with their position or the Commonwealth’s pursuit of a conviction.

That is how the adversarial system is supposed to work. And today, it worked.

Facing OUI Charges in Massachusetts?

If you’ve been charged with OUI—especially a second or subsequent offense—do not assume that a breath test result above .08 means automatic conviction. The science behind these machines is more uncertain than most people realize, and that uncertainty creates reasonable doubt.

Call the Law Office of Michael Patrick Murray, P.C. at (508) 393-4162 for a free consultation.

Attorney Michael P. Murray, defends clients facing OUI charges throughout Worcester County and Massachusetts. Results vary by case. Prior outcomes do not guarantee future results.