How to Discredit Retrograde Extrapolation in a DWI Breath Test Case »

May 15, 2010

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When a driver agrees to submit a DWI/DUI breath test, then the state’s star witness at the trial would be the technical supervisor and the state’s expert on the breath test machine. The state’s expert’s testimony will be the calculation of the driver’s alcohol concentration at the time of driving and how many drinks took him/her to that point. This specific scientific theory is called retrograde extrapolation.

As the prosecutor will ask the technical supervisor to determine these numbers for the jury. The technical supervisor at the witness stand will punch numbers into a calculator. All of sudden testimony looks dramatic when the state’s expert will be asked on cross examination whether he and the prosecutor discussed his testimony before he took a stand. After being asked, he will be forced to admit that he calculated the numbers ahead of time. Click here to read more »

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10 DWI/DUI Myths and Their Facts – Part-3 »

June 18, 2009

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Myth # 8:

Law enforcement officers can’t influence the BAC reading of a breath-testing machine.

Fact:

Law enforcement officers can and do influence BAC readings. Law professor and lawyer Lawrence Taylor quotes Dr. Michael Hlastala, Professor of Physiology, Biophysics and Medicine at the University of Washington. He said that, By far, the error which is most overlooked in breath testing for alcohol is the pattern of breathing…. During the breath the concentration of alcohol changes considerably… After discarding the dead space, the first part of the breath, has an alcohol concentration much lower than the equivalent BAC. Whereas, the alcohol concentration of the last part of the breath is much higher than the equivalent BAC. The last part of the breath could be over 50% above the alcohol level….Thus, it maybe indicated by a breath tester reading of 0.14% which has been taken from the last part of the breath that the blood level is only 0.09%.

It has been explained by Professor Taylor that, many police officers are aware of this error. They also know that if the machine opposes their judgment that the person they arrested is intoxicated, then it will effect their reputation.

Click here to read more »

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