How we defend motor vehicle homicide OUI cases in Massachusetts begins with understanding that the Commonwealth must prove far more than the fact that a fatal accident occurred. A motor vehicle homicide OUI charge under G.L. c. 90, § 24G is one of the most serious driving offenses in the Commonwealth: a felony that can carry years in state prison, a 15-year license loss, and the weight of a tragedy that the prosecution will work hard to lay at your feet. But “serious” doesn’t mean “indefensible.“
These cases are built on three pillars: proof of impairment, accident reconstruction, and causation. Every one of those pillars can be attacked, and in many cases, more than one collapses under scrutiny. A successful defense often requires challenging the reliability of field sobriety evidence, exposing flaws in the accident investigation, and demonstrating that factors unrelated to impairment contributed to the crash. Understanding how these cases are prosecuted—and how they can be defended—is critical when your freedom and future are at stake.
Challenging The OUI Evidence
The Commonwealth must prove impairment beyond a reasonable doubt, and the evidence is rarely as airtight as the police report suggests.
Breathalyzer results are a common pressure point. After Commonwealth v. Ananias, the reliability of the Draeger Alcotest 9510 came under sustained challenge, and calibration records, certification of the operator, and the source code of the device itself are all fair game. A breath test administered outside protocol, or on a machine with documented calibration drift, can be excluded entirely.
Field sobriety tests are equally vulnerable. The Horizontal Gaze Nystagmus, walk-and-turn, and one-leg-stand tests are validated only under specific conditions, and accident scenes almost never meet them. Gravel shoulders, flashing cruiser lights, traffic noise, injuries from the crash itself, fatigue, medical conditions, and footwear all degrade performance. A driver who failed the walk-and-turn on a sloped breakdown lane after a collision is not the same data point as a driver who failed it in a controlled training environment.
Rising BAC is another underused defense. Alcohol takes time to absorb, and a blood or breath sample drawn an hour or more after the crash may reflect a BAC higher than what the driver had behind the wheel. With the right expert and a clear timeline, retrograde extrapolation can support a real argument that the driver was below 0.08 at the time of operation.
Hospital blood draws bring their own problems. Chain-of-custody documentation, the type of swab used, the qualifications of the person drawing the blood, and compliance with G.L. c. 90, § 24(1)(e) all matter. A blood draw obtained without a warrant, outside the implied consent framework, or with sloppy documentation can be suppressed.
Challenging the Accident Reconstruction
The State Police Collision Analysis and Reconstruction Section (CARS) produces reports that read like settled science. They aren’t. CARS reconstructionists make assumptions about the coefficient of friction, perception-reaction time, point of impact, and pre-impact speed, and every assumption is a place to push back. We retain independent reconstruction experts to audit the methodology, recalculate the math, and identify where the Commonwealth’s expert reached beyond the data.
Event data recorder (EDR) downloads, the so-called “black box,” are increasingly central to these cases. EDR data can corroborate the defense theory just as easily as it supports the prosecution. Pre-crash speed, throttle position, brake application, and steering input all tell a story, and that story sometimes contradicts the trooper’s reconstruction. Tire friction testing, skid analysis, and lighting studies can all reframe what actually happened in the seconds before impact.
Cross-examining a CARS reconstructionist requires preparation. These are experienced witnesses, but their conclusions rest on inputs that can be questioned line by line.
Attacking Causation
Even if impairment is proven, the Commonwealth must show that the defendant’s operation was the proximate cause of death. That’s a separate element, and a frequent weak point.
- Was the other driver speeding, distracted, or running a red light?
- Was there a mechanical failure (brakes, tires, steering) unrelated to the defendant’s conduct?
- Were road conditions, signage, or visibility a factor?
- Did the victim’s own conduct break the chain of causation entirely?
Massachusetts law recognizes that intervening causes can defeat the causation element. If a jury concludes that someone or something other than the defendant’s impairment was the real cause of the collision, the homicide charge fails regardless of the BAC.
Suppression Motions
Before trial, we look hard at every piece of evidence the Commonwealth plans to use.
- Was the stop lawful?
- Was the arrest supported by probable cause?
- Were Miranda warnings given before custodial questioning?
- Was the blood draw constitutional?
A successful motion to suppress can gut the prosecution’s case before a jury is ever empaneled.
The Bottom Line
Motor vehicle homicide OUI cases are won in the details. The Commonwealth has investigators, reconstructionists, and toxicologists. You need a defense team that knows how to challenge them on their own ground. If you or a loved one is facing criminal charges in Eastern Massachusetts, contact the Law Office of Matthew Peterson today for a free consultation.
