An attorney preparing a DUI /DWI defense typically makes several motions designed to aid a driver’s prospects before a case gets to trial. A pretrial motion is a formal request to the court to order a certain action. A motion to have a blood or urine sample split to allow independent testing by a forensic expert is a common pretrial motion in a drunk driving case.

Prosecutors rely heavily on chemical test results in a driving under the influence case. A chemical test result that shows .08 percent or greater blood alcohol content (BAC)  – the legal limit for driving – is typically the evidential centerpiece in a DUI / DWI prosecution. However, chemical tests can also be a potent weapon for the defense.

Many chemical tests are given an hour or more after the driver is pulled over, and blood alcohol levels can rise significantly during that time. It’s not illegal to have a BAC of .08 percent or greater hours later at the police station – only when behind the wheel. An independent forensic expert may be able to establish that the driver’s BAC at the time of driving was not above the legal limit.

If a motion to split a blood or urine sample is granted, the defense attorney will send the split to a private, independent lab for testing.  A forensic toxicologist will analyze the driver’s BAC and determine whether proper testing procedures were strictly followed. 

This type of inquiry can be extraordinarily fruitful. Chemical test samples must be collected under strict guidelines, and any variation from that protocol can result in errors.  Blood samples should be drawn with sterile, dry hypodermic needles and a syringe or a clean, dry vacuum type container.  The technician cannot use alcohol to clean the driver’s skin where the blood is drawn, or the equipment used in the collection.  Additionally, the blood must be drawn into a tube containing a mixture of anticoagulant and preservative. If the levels of the anticoagulant and preservative are not correct, the results of the tests may be invalid. 

The original blood or urine sample in a DUI / DWI case sometimes gets lost or destroyed. Although police and prosecutors are not required to collect evidence that benefits the defendant, once the evidence is collected, they have a duty to preserve it. If the prosecution neglects to preserve that evidence, a skilled drunk driving lawyer will request sanctions which may result in the exclusion of the evidence or the dismissal of the case.

However, in order to win sanctions or a dismissal, the defense must prove that the police or prosecution acted in bad faith. If bad faith cannot be established, then the defendant is entitled only to recognition that evidence that may have pointed to his or her innocence has been lost.