Here is an email question recently received from a new lawyer:
I hope all is going well. I had a question regarding retrograde extrapolation. I was told that the statute says we cannot use retrograde extrapolation. So if a person blows a pbt of .06 at 12:30, and refuses the data master at the station (forgetting about all the implied consent stuff), and cops get a warrant and take person to clinic, and at 1:45 the blood reveals a .10, I was told that retrograde extrapolation is no longer valid because of statutory law, and that the person is presumed to be .10 at the time of the incident. Is this correct? I have been trying to look this up.
Here is our answer:
What crazy person told you that?? It’s preposterous really. The instruction was changed so it says there’s an inference BAC at time of test is same as at time of driving, but what this person is suggesting is that this change creates a presumption, which is not permissible. (Almost) the only presumption in a criminal case is the presumption of innocence.
Lawyers handling a lot of DUI cases might consider purchasing the BAC-Tracker software. This software assists in alcohol calculations, including retrograde extrapolation. The software is provided by BAC-Tracker International, Inc. Their web site indicates:
We are a forensic consulting company providing forensic alcohol litigation services internationally to the criminal justice community. Headquartered in Atlanta, Georgia, BAC-Tracker International, Inc. provides training, expert witness consultation, and software solutions for the extrapolation of blood alcohol concentration (BAC) and the management of scientific uncertainty for alcohol related cases.
BAC-Tracker International, Inc. has just completed their update to BAC Tracker software v3.1. A. This update offers a number of additional improvements. The most significant improvements include (1) the addition of a new report type – The Retrograde Alcohol Extrapolation Report. This report will extrapolate the alcohol level to a time of interest from a known BAC; (2) greater freedom of generating reports using various combinations of volume distribution formulae while accounting for uncertainties associated with absorption and/or elimination; (3) and the ability to include the uncertainty associated with the known BAC based on QA/QC data of the analytical method thus allowing BAC Tracker to account for every major source of uncertainty in the extrapolated result.
BAC Tracker v3.1 offers users the ability to generate up to 506 different reports using various combinations of volume distribution formulae while accounting for absorption rates and/or elimination rate uncertainties.
The software can be purchased from the manufacturer’s web site.