In August 2020, Delilah Diaz was arrested when she drove her boyfriend's car, laden with over $350,000 of hidden methamphetamine, across the U.S. border from Mexico. Her criminal trial tested the permissible scope of expert testimony as to a defendant's intent, ultimately resulting in a decision by the U.S. Supreme Court that has significant implications for criminal cases far beyond the specifics of her drug-trafficking case.

In Diaz v. United States, 144 S.Ct. 1727 (2024), the court held that expert testimony in a criminal case, as to whether "most people" similar to the defendant have a particular mental state, does not run afoul of Federal Rule of Evidence 704(b)'s prohibition against expert opinion evidence about whether a criminal defendant had or lacked the mental state required for conviction. Particularly in white-collar cases, where the defendant's intent is often the central disputed issue, the implications of Diaz may be far-reaching.

'Diaz: "Most People" vs. the Defendant

Diaz was stopped at the U.S.-Mexico border, where officers found 54 pounds of methamphetamine hidden in her car, which she claimed belonged to her boyfriend, who had loaned her the car to drive home to California. Charged with importing methamphetamine, Diaz claimed ignorance of the drugs.