Scientific Evidence and DWI

Once a charge for DWI enters a trial phase, one of the most important aspects of that trial will likely be the scientific evidence that is presented to the jury. Scientific evidence is the kind of evidence presented at trial by a scientist or other expert based on a scientific theory.

This kind of evidence is particularly important in DWI cases because of the nature of a DWI investigation. Soon after being arrested for DWI or after being pulled over, the police will take either a breath sample, blood sample, or both. Those samples, once taken and stored, do not act as evidence unless they are tested. The tests done on those samples are done under a scientific theory developed by experts to detect alcohol levels.

This kind of evidence is key to getting a conviction for DWI in most cases. The law in Texas and most states defines drunk driving as driving with a blood alcohol content above .08. Once the state can show a person’s blood was above that level when driving, the conviction is easy to get. The state cannot bring that evidence to trial without following the proper procedures.

DWI Appeal Denied

Those procedures used to present scientific evidence are a big part of how to defend a DWI case. Some might call this taking advantage of loopholes or being overly focused on procedure and not merits, but only by following the right rules regarding how evidence is presented to a jury can we be sure that the evidence is reliable. When the issue of a criminal conviction, record, fines, and jail time at are stake, every piece of evidence should be scrutinized heavily.

In a recently decided appeals case, a man convicted of DWI challenged how these procedures were observed at his DWI trial. He was arrested on suspicion of DWI last year after the police were called because he had urinated on a person’s lawn, driven away, and failed to use a turn signal. After failing a field sobriety test his blood was drawn and tested for alcohol content.

At trial, an expert was called on by the state to present evidence about what his blood alcohol content would have been while driving. They do this using a theory called retrograde extrapolation. But before a scientific theory can be presented to the jury, the expert and side putting the evidence in must show three things:

  • The theory is valid;
  • The technique proving the theory is valid; and,
  • The technique was properly applied to the situation.

In this case the court ruled that all of the above three steps were taken at trial, and so the appeal was denied. But it shows how technical the process is for admitting scientific evidence, and how the right legal team can many times thwart the state’s efforts to get a conviction for DWI.

At the Wilder DWI Defense Firm we know everything there is to know about challenging scientific evidence in a DWI trial. We have the experience, ability, and desire to aggressively defend your charges. If you are facing DWI charges in the Dallas area, consider contacting us so we can help you defend your charges. Contact us today.

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