There are some situations in which a person’s blood-alcohol level is tested hours after a car accident has taken place. The blood-alcohol content (BAC) is determined to be below Colorado’s legal threshold of .08 percent, yet the driver is regardless charged with DUI.
When the matter goes to court, the prosecutor argues that even though the BAC was below the legal threshold, the evidence shows that the driver was drunk at the time of the accident rather than at the time of the test. The prosecutor says that by using retrograde extrapolation, we can use science to essentially look backwards in time. Criminal defense attorneys have criticized retrograde extrapolation as junk science based on assumptions and opinions.
In a recent article in an insurance industry publication, an Ohio DUI defense said, “(Prosecutors) and puppet scientists know retrograde extrapolation is hogwash and will say so when it benefits them, but mostly they pretend otherwise because it is useful in gaining convictions.”
The process of retrograde extrapolation is a simple one that begins with what is known about alcohol. When a person drinks it, their BAC rises as it is absorbed into their system. Their blood-alcohol level at some point hits and peak and then decreases as the body processes and eliminates the alcohol.
For example a prosecutor might argue that because Person A had a blood-alcohol level of 0.06 percent when tested at midnight, his BAC must have been .12 percent four hours earlier when the acccident took place. But the prosecutor’s deduction requires a number of assumptions on his or her part.
We will get into that portion of the criticim of retrograde extrapolation in our next post. Please be aware that if a Denver prosecutor is trying to use the dubious math in your case, a skilled defense attorney knows how to challenge this problematic “evidence.”