Plymouth County District Attorney Timothy J. Cruz, whose office filed an amicus curiae brief in the case, said it would have been unduly burdensome to require prosecutors to call an extrapolation expert in every OUI trial.

"It wasn't the intent of the Legislature to make it more difficult to prove these cases, but until now the statute was being interpreted that way," he said. "A lot of us recognized this was going to be a seminal case in the commonwealth. I think a good number of judges and lawyers were waiting for this decision, which really does provide the clarity that was needed."

While Cruz said he still expects the defense to aggressively attack the admissibility of breath-test evidence, he noted the extrapolation expert question has now been clearly answered.

OUI defense lawyer Randy S. Chapman of Chelsea, who attended the oral arguments, said he was not surprised by the ruling but questioned the court's setting of the three-hour time limit.

"The test that's being admitted two or three hours later is not going to reflect what the person's blood alcohol level was at the time of operation, which is what the statute requires," he said. "This is another example of an inherent flaw in the legislation, which is typical of the drunk-driving law [that] has been amended close to 20 times over the past 15 years."

Assistant District Attorney Judith Ellen Pietras, who argued the case on appeal, and Stephen B. Monsein of Amherst, who represented the defendant, could not be reached for comment prior to deadline.

In April 2005 at 9:10 p.m., the defendant, Anne Colturi, was stopped by a Massachusetts state trooper.

The trooper had seen her driving in an unsafe manner and pulled her over. When he approached, the trooper smelled alcohol on the defendant.

During a conversation with her, he observed that her speech was slurred and her eyes were glassy. Further, he noted that she was unsteady on her feet and used her car for support as she walked to the rear.

When the trooper arrested her for OUI, the defendant consented to a breath test. As required by law, two tests were then administered.

The first test was taken at 10:15 p.m. and the second at 10:19 p.m. The results showed a blood alcohol level of .15 percent.

A complaint then issued against the defendant, charging her with violating the OUI statute by operating a vehicle "with a percentage, by weight, of alcohol in his or her blood of eight one-hundredths or greater, or while under the influence of intoxicating liquor."

When the defendant moved in limine to exclude the admission of the breath-test results without the testimony of an expert on extrapolation, District Court Judge David S. Ross granted the request. The commonwealth then appealed.

Cordy said an impractical set of burdens would be placed on prosecutors should the position taken by the trial judge be affirmed.

"It is … undisputed … that numerous OUI cases are prosecuted every day in courts throughout the Commonwealth, that there are few State employed experts on retrograde extrapolation available, and that the costs of utilizing private experts at these trials would be inordinate," he pointed out.

In addition, the judge said that, in most cases, prosecutors would not be able to acquire the data needed to construct an accurate retrograde extrapolation because such information would almost always be in the possession of defendants and protected by their constitutional right to remain silent.

Cordy turned to the legislative intent of the statute and found it was designed to strengthen the protections afforded the public from drivers who might be driving while impaired by alcohol.

"If the Legislature had intended to change our existing rule of admissibility when it amended the OUI statute … and to place additional and even 'impossible' burdens on the Commonwealth, it would have said so explicitly," he said.

Having added the per se language to the statute, the Legislature deleted wording that had previously created a "permissible inference" that a person with a .08 or higher was under the influence, Cordy noted.

"It is in this context that we examine whether the Legislature also intended to change the law with respect to the admissibility of breathalyzer test results to make it more difficult for the Commonwealth to present what has otherwise been considered relevant and highly reliable evidence of the level of alcohol in the blood of a driver arrested for OUI," he said.

Cordy observed that SJC decisions prior to the enactment of the 2003 amendments rejected attempts to exclude breath-test results due to the lapse of time between the alleged offense and the administration of the breath test. In doing so, he explained, the court had consistently ruled any delay in the administration of the test went to the weight, not the admissibility, of the evidence.

But Cordy cautioned that the SJC's ruling was limited to only those cases where a breath test was conducted within a reasonable period of time after a driver had operated the car.

While other states have expressly established what constitutes a "reasonable period," Cordy said the Massachusetts statute and caselaw until now had been silent on the subject. In arriving at a three-hour rule in this case, Cordy said the other states' statutes served as a useful guide.

"The facts and circumstances in particular cases may [however] establish that a lesser or greater time period ought to be applied," he said.