What Is Evidence in a Seattle DUI Case?

To convict someone of DUI in Washington, the State must prove guilt beyond a reasonable doubt. Prosecutors do not rely solely on the arresting officer's testimony. Instead, they present multiple forms of evidence intended to show that the driver was impaired or over the legal limit at the time of driving.

Understanding the types of evidence commonly used in DUI cases can help you better evaluate your defense options.

Common Types of DUI Evidence

DUI cases often involve several categories of evidence, including:

  • Field sobriety test performance
  • Breath test results
  • Blood test results
  • Officer observations (odor of alcohol, red eyes, slurred speech)
  • Dashcam or body camera footage
  • Statements made by the driver
  • Accident reports or witness statements

In many cases, prosecutors rely heavily on chemical test results and officer observations.

Field Sobriety Tests

Field sobriety tests (FSTs) are physical coordination exercises administered roadside before arrest. These may include the walk-and-turn test, one-leg stand test, and horizontal gaze nystagmus test.

In Washington, drivers may decline field sobriety tests without additional criminal penalties. However, an officer may still arrest a driver based on other observations.

Chemical Tests and Implied Consent

Chemical tests measure alcohol or drug concentration in a person's system through breath or blood analysis. Under Washington's Implied Consent law, drivers who are lawfully arrested for DUI are required to submit to a breath test. Refusal can result in administrative license suspension and may be used as evidence in court.

In Washington, a driver may be charged with “per se” DUI if, within two hours of driving:

  • The alcohol concentration is 0.08 or higher (for drivers 21 and over)
  • The THC concentration is 5.00 ng/mL or higher (for drivers 21 and over)

Even if a driver is below these limits, prosecutors may still attempt to prove impairment based on other evidence.

Other Evidence Prosecutors May Use

DUI cases are rarely based on one piece of evidence alone. Police officers are trained to document behavioral cues such as:

  • Driving pattern prior to the stop
  • Difficulty producing documents
  • Confusion or inconsistent answers
  • Odor of alcohol or marijuana
  • Open containers or substances found in the vehicle

If an accident occurred, that fact may also be presented to suggest impairment.

Challenging DUI Evidence

Every type of DUI evidence can be examined and challenged. Field sobriety tests are subjective and can be affected by fatigue, medical conditions, uneven road surfaces, or stress. Breath and blood tests must be properly administered, calibrated, and documented according to strict procedural requirements.

An experienced DUI defense attorney reviews:

  • Whether the traffic stop was lawful
  • Whether proper arrest procedures were followed
  • Whether testing equipment was properly maintained
  • Whether testing protocols were followed
  • Whether constitutional rights were respected

If procedures were not followed, evidence may be suppressed or its reliability questioned at trial.

Seattle DUI Defense Representation

DUI cases are evidence-driven. The strength of the State's case often depends on technical details and procedural compliance.

Attorney Steve Karimi is a former Washington State prosecutor who understands how DUI evidence is built and how it can be challenged. If you are facing DUI charges in Seattle, contact our office to discuss your case and review the evidence involved.