The Supreme Court ruled in a six-to-three opinion against a drug mule fighting conviction by claiming expert testimony from a Homeland Security Investigations (HSI) special agent violated federal evidentiary rules.

In 2020, Delilah Diaz was stopped at a Port of Entry at the United States-Mexico border. Border Patrol agents searched her vehicle and found more than 54 pounds of methamphetamine. Diaz was subsequently charged with importing methamphetamine, requiring federal prosecutors to prove that she was aware that she was importing drugs to the U.S. via the border.

At trial, Diaz claimed she was unaware the methamphetamine was hidden inside her car. Federal prosecutors, in response, had HSI Special Agent Andrew Flood testify as an expert witness in the case. He argued that drug traffickers typically do not entrust large amounts of drugs with couriers who are unaware they are transporting such drugs.

Diaz claimed Flood’s testimony violated federal evidentiary rules, claiming he was stating an opinion about her mental state or condition. The court allowed Flood to testify that most couriers are aware they are transporting large amounts of drugs in similar cases.

In the case, a jury convicted Diaz, who appealed the decision on the basis that Flood’s testimony violated federal evidentiary rules. The Court of Appeals upheld the conviction.

On Thursday, Justice Clarence Thomas wrote for the majority, finding that Flood’s expert testimony was not an opinion and thus did not violate federal evidentiary rules:

In this case, Agent Flood did not express an opinion about whether Diaz herself knowingly transported methamphetamine. Instead, he testified about the knowledge of most drug couriers. That opinion does not necessarily describe Diaz’s mental state. Because Agent Flood did not express an opinion about whether Diaz herself knowingly transported methamphetamine, his testimony did not violate Rule 704(b). [Emphasis added]

Diaz’s counterarguments are unpersuasive. She first argues that Agent Flood functionally stated an opinion about whether she knowingly transported drugs when he opined that most couriers know that they are transporting drugs. But an opinion about most couriers is not an opinion about all couriers. Agent Flood asserted that Diaz was part of a group of persons that may or may not have a particular mental state. The ultimate issue of Diaz’s mental state was thus left to the jury’s judgment. Diaz next relies on dictionary definitions of “about” to argue that Rule 704(b)’s phrase “state an opinion about” includes all testimony that “concerns” whether the defendant had a particular state of mind. That text’s surrounding context, however, makes clear that Rule 704(b) addresses only conclusions as to the defendant’s mental state. Rule 704(a) further confirms the narrow scope of testimony prohibited by Rule 704(b). Because Rule 704(b) is an “exception” to Rule 704(a), Rule 704(b) can only be understood to cover a subset of the testimony that Rule 704(a) expressly allows, which is opinion testimony that includes ultimate issues. Diaz’s reading would have the exception swallow the rule. [Emphasis added]

Thomas was joined by Chief Justice John Roberts, as well as Justices Samuel Alito, Brett Kavanaugh, Amy Coney Barrett, and Ketanji Brown Jackson, who filed a concurring opinion. Justice Neil Gorsuch filed a dissenting opinion, joined by Justices Sonia Sotomayor and Elena Kagan.

The case is Diaz v. United States, No. 23-14 in the Supreme Court of the United States.

John Binder is a reporter for Breitbart News. Email him at jbinder@breitbart.com. Follow him on Twitter here.