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Evidence of BAC in Utah DUI Trial

Is a prosecutor required to present scientific evidence of BAC to prove DUI?

A prosecutor may request that a trial judge give a jury instruction that explains that the prosecutor is not required to introduce "scientific evidence" in order to meet the burden of proving the case beyond a reasonable doubt. These instructions are sometimes referred to informally as a "CSI" instruction, and are designed to try to counteract the effect that modern television crime dramas have had on juror's expectations.

DUI Attorney Salt Lake City, UtahA CSI instruction may be a valid statement of law and may make sense in some cases. For example, in a bike theft case we would not expect the police to swab for touch DNA or take fingerprints . . . when the officer personally saw the defendant riding the bike away from the bike rack as the owner yelled "stop thief!" Police departments have limited scientific resources, and should not be required to expend those resources in cases where scientific evidence is unnecessary. But in a DUI case, the legislature has enacted a statute that begs for scientific evidence.

What evidence is required to prove a DUI?

A charge under Utah Code 41-6a-502 provides alternative methods by which a prosecutor can prove a DUI. One method requires no evidence of a specific determinable BAC (blood or breath alcohol concentration); it requires only proof that the person was impaired by alcohol or drugs to a degree that the person was not able to safely operate a vehicle. A prosecutor usually attempts to prove this impairment by introducing evidence of a bad driving pattern (swerving, failing to stay in one lane, etc.) or by evidence of an actual accident.

A more common method of proving DUI is to prove a BAC of 0.05 or greater. (NOTE - As of January 1, 2019, Utah's per se DUI limit was changed from 0.08 to 0.05.) This method puts the prosecutor at an advantage, because no proof of any actual impairment is required. Instead, the DUI charge can be supported based just on evidence of a BAC of 0.05 or greater. But proof of BAC requires scientific testing.

Is an estimate of BAC sufficient to prove DUI?

Police officers are trained in many areas of investigation that involve processes of estimation. An officer may receive training in estimating the speed of a moving vehicle, based on visual observations of the vehicle as compared with a stationary background or as compared to the officer's own speed. An officer may be trained in estimating the weight of package of marijuana, based on the volume or heft of the package.

But there is no way to make an accurate visual estimate of BAC, no way to visually analyze a blood sample to determine BAC, and no way to accurately estimate BAC based merely on the odor of alcohol on a person's breath. A person who "holds their alcohol well" might easily have a BAC of more than twice the legal limit yet still not show immediately obvious signs of impairment. Yet another person with a much lower BAC could show much greater visual indicators of intoxication.

Determining the actual blood or breath alcohol level requires scientific testing to get real numbers. So asking for scientific evidence in a DUI trial is not at all unreasonable.

What about FST's? Can they support proof of BAC in a DUI trial?

The NHTSA standardized field sobriety tests (FST's like the walk-and-turn, one-legged stand, and horizontal gaze nystagmus) can be used to support probable cause to arrest for DUI. But these FST's support only a probability that a person may be above a certain BAC. There are conditions and situations that can cause a 100% sober individual to still fail the FST's. Failure on the FST's, by itself, is not sufficient to establish proof beyond a reasonable doubt for a DUI conviction. But a person's performance on the FST's can be considered by a jury or judge.

Is a CSI-type instruction appropriate in a DUI trial?

Courts give the CSI instruction to help jurors understand the difference between fictional television drama and the real world. In the real world, police don't swab every surface for DNA; police don't bring a black light to every hotel room crime scene; police don't do fiber analysis on every piece of clothing; and computer photo enhancement usually doesn't produce a legible license plate.

But in a DUI case, police officers can and regularly do administer breath tests or take blood or urine samples for the lab to test. And even when a suspect refuses to submit to the test or to have a sample taken, police officers can and regularly do get warrants so that they can take whatever kind of sample they need to take in order to properly do their job.

The CSI instruction may be just fine for helping juries understand the difference between Hollywood and reality. But a CSI instruction should not be used to excuse the police from failing to do their jobs. Sure, a prosecutor can proceed on the argument that, regardless of BAC, the person was not able to safely operate the vehicle. But the judge should not instruct the jury in a way that essentially gives the police a pass for not bothering to get a sample to test.

Finding a DUI Attorney in Utah

Utah Criminal Defense LawyerIf you are facing prosecution for DUI, driving with measurable metabolite, or other alcohol- or drug-related charges in Utah, it is vital that you consult with and obtain the assistance of an experienced criminal defense attorney. The Utah criminal justice system is complex and the penalties for DUI and related charges can be severe. The right defense strategy and the right criminal defense attorney can make all the difference.

Contact us today to see how we can help you.


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Serving Salt Lake, Davis, Weber, Utah, Cache, Tooele, Summit, Box Elder, and Wasatch Counties, and all of Utah.

Attorney Stephen Howard practices as part of the Canyons Law Group, LLC and Stephen W. Howard, PC.

Offices in Salt Lake and Davis Counties
560 South 300 East, Suite 200, Salt Lake City, UT 84111
952 S. Main St., Suite A, Layton, UT 84041

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In Salt Lake City, call 801-449-1409.
In Davis County, call 801-923-4345.

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