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DWI Defense Project Seminar – Live Blog – Cross Examining the State’s Expert in a Breath Test Case

So far, the best lecture has been put on by Attorney Mimi Coffee.  Mimi practices in Ft. Worth, and also Dallas, I believe.  

She went over how to knock a breath test down, piece by piece, and get show how low the score could be. Her speech was a significantly easier topic, considering Texas uses the old and outdated Intoxilyzer 5000.

First, you go through the setup stage during your cross examination.

– Always give the D the benefit of the doubt:  This is done mostly in voir dire.  Usually the experts that I’ve seen will say that they go with the lower score "to give the benefit of the doubt."

– Dont know what the 3rd blow would be:  Most will readily agree with this.  We don’t know what the 3rd blow will be.

– set up .02 margin of tolerance, precision:  This one is pretty easy to set up as well.  With the Intoxilyzer 5000, Both breath samples must be within .02 of each other to get a valid result. (Interestingly enough, in Oklahoma, it is .03.  I never knew that).

– not possible to metabolize .01/.02 in 2 minutes:  If the 2 scores are off of each other, you should establish that this isn’t the person metabolizing the alcohol within a few minutes of the test.  Usually the 2 "subject samples" are not equal.  The State’s witness will always agree with this.

– up down variance in 2 scores does not show metabolism:  One common misconception of juror is that you can tell if someone’s BAC is going up or down which correlates to the 2 subject samples going up and down.  I have seen prosecutors in Collin county say "you see how the 2nd breath score is lower than the first?  That means his BAC was going down — therefore, his BAC was higher at the time of driving!"  I’m not sure if they were purposely lying, or just green, but either way, even the State’s expert will agree this is false.

.01 predicted value must agree with actual value:  This is for the reference sample.  The reference sample is mixed up to supposedly be .08.  As long as it is within .01, the intoxilyzer 5000 says "OK".

-retrograde / # of drinks in a normal drinking spree one would have to consume (not what’s present in one’s system):  You may be able to get the breath score lower by successfully arguing that your client was lower at the time of driving.

– air blank is not .000:  Apparently when the machine says .000, it’s not really .000.  Depending on what expert you get, .000 can actually be as high as .009.  (Some experts will say .005).

– Dr. AW Jones, breath temperature: According to Dr. Jones, breath score can be affected by the breath temperature.

– Tolerance – "Texas Breath Alcohol Testing Program Operator Manual, ethanol section, p.47 — has the actual definition.  Basically, you cant fake a BAC.  Tolerance wont affect the score.

The below example is based on a .14 breath test:

Defendant’s Breath Score  .014
Intrinsic Margin -.010
Margin of Tolerance -.020
Air Blank Fallacy -.009
(.6.5%* (37degrees – 34 degrees).140) -.027
Scientifically giving benefit of doubt to a Defendant -.074


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