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MINNEAPOLIMEDIA NEWS | Minnesota Supreme Court Clarifies Breath-Test Evidence Rules in DWI License Revocation Cases
The court ruled that an imperfect observation period does not automatically invalidate a breath-test result, requiring judges to examine evidence of possible contamination before determining admissibility.
ST. PAUL, MN (November 14, 2026).
The Minnesota Supreme Court has clarified the legal standard governing challenges to breath-test evidence in drunken-driving license revocation proceedings, ruling that an inadequate observation period does not automatically require exclusion of a test result.
The decision, issued Thursday, November 12, requires district courts to evaluate all relevant evidence concerning whether a breath sample may have been contaminated before determining whether the result can be admitted.
The ruling arose from the case of Derek Alexander Knapp, whose driver's license was revoked after a breath test registered an alcohol concentration of 0.08. Knapp challenged the revocation, arguing that the arresting officer had not conducted an adequate observation period before administering the test.
A district court agreed that the observation was insufficient and rescinded the revocation. The Minnesota Court of Appeals subsequently reversed that decision, prompting review by the state's highest court.
The Supreme Court vacated the appellate decision and returned the case to the district court for reconsideration under the clarified legal standard. The justices did not make a final determination about whether Knapp's breath-test result should be admitted.
The dispute concerned procedures intended to ensure that breath-testing instruments measure alcohol concentration accurately. Such instruments are designed to analyze air exhaled from deep within the lungs, but alcohol remaining in a person's mouth can affect the reliability of a sample.
Officers are therefore trained to observe individuals before administering breath tests. The observation period is intended to identify events such as vomiting or belching that could introduce mouth alcohol and potentially produce an inaccurate result.
In Knapp's case, the arresting deputy testified that he had been trained to conduct a 15-minute observation period and had monitored Knapp while the two were in a squad car and later at a jail.
The district court questioned whether the deputy had been able to maintain adequate observation throughout that period. The officer had viewed Knapp through a rearview mirror while separated from him by a partition, and the court also expressed uncertainty about the officer's position during portions of the observation at the jail.
Those circumstances led the district court to conclude that the test result lacked sufficient reliability. The Supreme Court, however, determined that the proper inquiry required consideration of whether the evidence established possible contamination rather than automatic exclusion based on the inadequacy of observation.
Writing for the court, Justice Paul Thissen explained that a deficient observation period can be relevant to reliability without necessarily establishing that a breath sample was contaminated.
Under the clarified standard, the test result must be admitted if the evidence establishes, by a preponderance of the evidence, that the sample was not contaminated. That standard requires a determination that the absence of contamination is more likely than not.
The decision does not eliminate the importance of observation procedures. Officers remain responsible for following practices intended to ensure reliable testing, and defendants may continue challenging results when evidence suggests that a sample could have been affected by contamination.
The ruling also rejects a burden-shifting framework previously applied by the Court of Appeals in this category of cases. Instead, district judges must examine the evidentiary record as a whole and make a direct determination about the reliability of the sample.
For law enforcement agencies, the decision reinforces the importance of documenting breath-test procedures and the circumstances surrounding sample collection. For motorists challenging license revocations, it clarifies that a procedural deficiency must be evaluated in relation to the evidence of possible contamination.
The Supreme Court returned Knapp's case to the district court, which may reopen the evidentiary record if necessary before determining whether the breath-test result should be admitted.
The ultimate outcome of Knapp's license revocation therefore remains unresolved. The broader legal significance of the decision lies in its clarification that an imperfect observation period does not automatically invalidate breath-test evidence.
The case, Knapp v. Commissioner of Public Safety, establishes guidance for future implied-consent proceedings in which the reliability of breath-test results is disputed.
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