The Supreme Court ruled that breath test results obtained without providing mouth rinse water to drivers during DUI checks cannot be used as evidence. The court determined that the procedure of offering mouth rinse water before a breath test is a legally binding regulation, and results collected in violation of this procedure should generally be excluded as evidence.
On October 25, the Supreme Court's first division, led by Justice Cheon Dae-yeop, overturned a lower court's ruling that sentenced defendant A to one year in prison with a two-year suspended sentence for violating the Road Traffic Act (drunk driving) and sent the case back to the Daejeon District Court.
A was charged with driving a cargo truck while intoxicated on a road in Sejong City in December 2023. Police responded to a report of a driver asleep in a running vehicle and measured A's blood alcohol concentration, which was found to be 0.081%, a level that would result in license suspension.
However, during the trial, A's defense raised significant concerns about the legality of the measurement process. They argued that the absence of mouth rinse water during the breath test led to a higher blood alcohol concentration reading due to residual alcohol in A's mouth.
According to regulations related to the Road Traffic Act and enforcement guidelines, police are generally required to provide a certain amount of drinking water to drivers before conducting a breath test to wash away any residual alcohol in the mouth.
Despite this, both the first and second trial courts sided with the police, sentencing A to one year in prison with a two-year suspension. The first trial court ruled that the mouth rinse water provision procedure was merely an internal guideline for police and that failing to follow it did not render the breath test itself illegal. Additionally, the court found that since the measurement occurred more than 20 minutes after drinking, the mouth rinse was not deemed essential, and the defendant bore some responsibility for the lack of water provision due to sudden actions.
However, the Supreme Court's ruling differed from the lower courts. It clarified that the previously internal guideline regarding the provision of mouth rinse water was officially codified in the Road Traffic Act enforcement regulations in July 2023, elevating it to a legally binding procedure. Therefore, breath test results obtained without following this formal procedure should generally be excluded as evidence to protect the defendant's fundamental rights.
Furthermore, the Supreme Court noted existing research indicating that residual alcohol in the mouth dissipates after 20 minutes post-drinking. It emphasized that the controlled experimental results, which excluded various variables such as burping, hiccups, and gastrointestinal issues, do not account for the potential for misinterpretation of blood alcohol concentration due to residual alcohol even after 20 minutes in real enforcement situations.
* This article has been translated by AI.
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