Supreme Court grants certiorari to an alleged drug courier (challenging a federal drug conviction) because the prosecution used an “expert witness” to rebut her defense that she didn’t know about the drugs that were hidden inside her car, which she said belonged to her boyfriend. Petitioner says the “expert” testimony violated Fed.R.Evid. 704(b).

The Supreme Court granted certiorari in Diaz v. United States, No. 23-14 (cert. granted, Nov. 13, 2023).

Discussions and relevant cert. papers are available here: https://www.scotusblog.com/case-files/cases/diaz-v-united-states/

The petition for certiorari frames the “Question Presented” as follows:

Federal Rule of Evidence 704(b) provides: “In a criminual case, an expert witness must not state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense. Those matters are for the trier of fact alone.” Fed.R.Evid.704(b).

The question is: In a prosecution for drug trafficking —— where an element of the offense is that the defendant knew she was carrying illegal drugs —— does Rule 704(b) permit a governmental expert witness to testify that most couriers know they are carrying drugs and that drug-trafficking organizations do not entrust large quantities of drugs to unknowing transporters?