12/06/2023 - US Supreme Court to Review the Extent of Expert Witness Testimony in Drug Trafficking Case

The US Supreme Court granted consideration to review the admissibility of expert witness testimony in proving intent in a drug trafficking case known as Diaz v. United States. Delilah Diaz, a California resident convicted of drug transportation, filed a petition for reconsideration, challenging her conviction based on the government's use of expert testimony contradicting her claim of ignorance about carrying drugs into the US.

Previously, the US Court of Appeals for the Ninth Circuit upheld Diaz's conviction for transporting methamphetamine across the US-Mexico border under 21 U.S.C. ยงยง 952 and 960. The lower courts deemed the government's expert witness testimony, asserting that most "blind mules" are aware they are smuggling drugs, admissible under Federal Rule of Evidence 704(b).

The issue at hand revolves around whether Rule 704(b) permits expert witnesses to testify that an individual transporting drugs was aware of doing so, leading to a circuit split. While the Ninth, Eighth, and Eleventh Circuits have allowed such testimony, the Fifth Circuit has consistently held that the rule prohibits opinions equivalent to prohibited opinions on an actor's knowledge and explicit opinions on the matter.

In her request for reconsideration, Diaz highlighted this circuit split and argued against the Ninth Circuit's position. She contended that the Ninth Circuit's stance contradicts the text of Rule 704(b), which prohibits all "opinions about" the defendant's mental state, not just explicit opinions. Diaz further asserted that this position lightens the government's burden of proving knowledge beyond a reasonable doubt, allowing a generalization about a specific class of defendants to substitute for evidence specific to the actual defendant.

Diaz ultimately argued that allowing such expert witness testimony violates "elementary notions of due process." The Supreme Court is anticipated to hold oral arguments on this matter next year.