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.