In a recent blog, I discussed a problematic decision by the Massachusetts Appeals Court in Com. v. Dacosta upholding a defendant's conviction on the charge of unlawful operation with a BAC of .08 or greater, when the defendant's BAC level was tested approximately an hour after the traffic stop. In so ruling, the Appeals Court denied the defendant the right to present "retrograde extrapolation" evidence, which may have relieved the defendant of criminal culpability in this case.
The defendant in Dacosta asked the trial judge to require the Commonwealth to present retrograde extrapolation evidence confirming that the defendant's BAC level did not rise between the time of the stop and the time the breath test was taken. Without such evidence, argued the defendant, no reasonable jury could infer the BAC level at the time the defendant was actually operating the vehicle. And since the jury convicted on a per se charge only, the conviction must be vacated since the Commonwealth failed to establish the defendant's precise BAC level at the time of operation. You can read the DaCosta decision by following this link.
The doctrine of retrograde extrapolation essentially stands for the scientific phenomenon whereby an individual's BAC level in the past can be determined from a later measurement by factoring the amount of alcohol consumed, the timing of the consumption, the individual's weight, and any food he may have eaten while or after he consumed the alcohol. In some instances where the doctrine is applied, the individual's BAC level at a point in time soon after consumption may be lower than the BAC level later in time. That is because BAC is a measure of the amount of alcohol that is absorbed in the blood at the time it is measured; as time passes, the body (liver) metabolizes and eliminates alcohol absorbed in the blood at a consistent rate, while the rate at which the alcohol is absorbed in the blood may vary depending on the amount of food consumed and the weight of the individual. Therefore, as in the Dacosta matter, the defendant's BAC may have actually been below the statutory limit at the time of operation an hour earlier than when he was tested, depending on his meal earlier that evening.
The science underlying retrograde extrapolation is not novel; it has been used by prosecutors across the nation to convict defendants on per se charges for several years. However, as the science developed over the years, it has advanced our knowledge of how alcohol is absorbed into the blood, and how rates of absorption may vary depending on several different factors. Because of these advancements, defense attorneys may now call expert testimony to present evidence that the defendant's BAC was actually lower at the time of operation than it was later in the evening due to the differing rates of absorption.
Although the defendant had no burden of proof by virtue of the fact that he is presumed innocent until proven guilty, the defendant's attorney may have opted to call his own expert witness to testify to the likelihood that the defendant's BAC level was actually below .08 at the time of operation. And since information on the defendant's weight, alcohol consumption, and meal earlier that evening can probably only be provided by the defendant himself, the Commonwealth would have likely failed to rebut this testimony.
The unfortunate reality I have encountered as an OUI Lawyer in Massachusetts
is that resources such as expert witnesses are not equally available to the Commonwealth and the defendant. Expert witnesses are rarely called by defendants in such cases because they are very expensive, and many defendants are indigent or simply unable to pay such high charges in addition to attorney fees and taking time off from work to attend court hearings. The only relief for individuals such as Dacosta, therefore, is for the SJC to review this Appeals Court decision, and require the Commonwealth to present expert testimony on the principles of retrograde extrapolation since the burden rests on the Commonwealth to establish the defendant's guilt if it chooses to prosecute.