In Thompson, the driver challenged his conviction of misdemeanor driving while impaired, arguing that the district court abused its discretion in denying his motion to discover the source code for the Intoxilyzer 5000EN. Under the Minnesota Rules of Criminal Procedure, in misdemeanor cases, any discovery beyond police investigatory reports is by consent of the parties or motion to the district court. Under the rule, the district court may exercise its discretion and require the prosecution to disclose material and information if the defendant shows that the information may relate to the guilt or innocence of the defendant or negate the guilt or reduce the culpability of the defendant as to the offense charged.

Thompson argued that the Intoxilyzer was “the State’s only witness” and asserted that he is entitled to “conduct a full examination” of this witness. He argued that he cannot assess the reliability of the testing method without access to the source code. He asserted that he has shown the relevance of the source code to his guilt or innocence in a manner sufficient to make the district court’s denial of its discovery an abuse of discretion. The Court of Appeals, however, disagreed, relying on the State’s expert, who stated:

In the field of forensic toxicology, validation of analytical methodologies for analyzing alcohol and other drugs in the human body is performed exclusively without access to analytical instrument software source code . . . . I have never heard or read of a validation of a toxicological analysis method that was performed with access to the software source code of the analytical instrumentation. I also am unaware of any articles in peer review journals describing the necessity for access to source codes for any validation tests.

Judge Stoneburner opined:

Thompson has not shown the existence of any validation method that requires the source code; has not explained why existing reliability testing (that does not require the source code) is insufficient to establish the reliability of the instrument used in his test; and has not explained how the source code could invalidate existing reliability testing. On this record, we cannot conclude that the district court abused its discretion by denying Thompson’s request for discovery of the source code.

Why do we defense lawyers continue to push for the disclosure of the Intoxilyzer source code? It’s actually pretty simple. The code is the hub between a breath sample and the method by which those samples are afforded a numerical value. Remember your math teacher demanding that you “show your work?” The Intoxilyzer manufacturer (obviously intending to protect what it believes to be valuable intellectual property) continues to refuse to show its work. How, then, can the court understand whether the results offered by a machine are inherently reliable?