As regular readers know, we wrote about retrograde extrapolation in our previous post. It’s a questionable bit of “science” that Denver-area prosecutors will sometimes use to try to argue that a person was drunk at the time of a car accident, even though no blood-alcohol test was taken at the time of the crash or its immediate aftermath.
A prosecutor will use the results of a blood-alcohol test done hours after the crash. When the BAC (blood-alcohol content) is lower than Colorado’s DUI threshold of .08 percent, the prosecutor will tell the court, “We know how quickly alcohol is metabolized and eliminated by humans and how that lowers a BAC reading. So it’s a simple matter of adding to the tested BAC the amount of alcohol we ‘know’ must have been absorbed and eliminated between the time of the accident and the time of the blood-alcohol test.”
There are several big assumptions that have to be made by the prosecutor in order to make that grand statement, however. For example, the prosecutor must know the amount and types of food the person ate before the accident and how those foods affect the rate of alcohol absorption into the person’s system. The prosecutor must also know the type of alcohol consumed and amount consumed and know how quickly that type and amount of alcohol is absorbed into the person’s system. Of course, the rate of absorption is also determined by the person’s gender, age, weight (at the time of the accident), height, and their state of mental and physical health.
In addition, the prosecutor must be able to show that they know when the person began drinking and when the person stopped and factor that into the alcohol absorption-elimination rate for the person in question considering all of the previously mentioned factors.
You can see why skilled, experienced Colorado criminal defense attorneys challenge retrograde extrapolation “evidence.” It is as one scientist put it, “the functional equivalent of a wild guess.”