Supreme Court grants cert on federal drug case concerning expert testimony on defendant's knowledge

This morning brings this new Supreme Court order list that finally has something interesting for criminal justice fans.  Actually, there are two matters of interest, a cert grant in a federal drug case and a lengthy dissent from the denial of cert in a state prison conditions case.  In this post I will cover the cert grant and follow up with a separate post on the cert denial.

The cert grant comes in Diaz v. US, and John Elwood here at SCOTUSblog effectively summarized this case last week after it prompted a relist:

Delilah Diaz was stopped returning from Mexico to her home in California.  Officers were suspicious that Diaz’s window made a “crunching” noise when she rolled it down, so they searched the car and found nearly 28 kilograms of methamphetamine — worth almost $400,000 — in the door panels.  Diaz said that she had borrowed the car from her boyfriend and did not know about the drugs.  At her trial, prosecutors called a law-enforcement agent as an expert witness to testify that in most cases, couriers know they are transporting large quantities of drugs across the border and that traffickers rarely risk the potential of large losses on “blind mules” — couriers who are unaware what they’re carrying. Diaz was convicted.

On appeal, Diaz argued that the testimony was inconsistent with Federal Rule of Evidence 704(b), which states that “[i]n a criminal 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,” which is a question “for the trier of fact alone.” The U.S. Court of Appeals for the 9th Circuit affirmed Diaz’s conviction.  It concluded that Rule 704 only bars expert witnesses from stating an express opinion about whether a particular person knew they were committing a crime, not from stating general opinions about similar defendants and the likelihood of their culpability.

Diaz has now petitioned the Supreme Court for review.  She argues that that the testimony would have been thrown out in the U.S. Court of Appeals for the 5th Circuit, which has held that such testimony is inadmissible.  The 5th Circuit, she notes, includes Texas and, therefore, nearly all of the rest of the southern border, and she argues that the conflict between two border states’ appellate courts must be resolved. The government acknowledges a “disagreement between the Fifth Circuits and other circuits” but it contends that any disagreement “does not warrant this Court’s review.”  The 5th Circuit’s test, the government claims, is heavily “fact dependent.”  The government also argues that any error from admitting the agent’s testimony was harmless because the evidence of guilt in Diaz’s case was strong, because her story was “flimsy”: She didn’t know where her supposed boyfriend lived or his phone number, and although she claimed to dislike driving at night, she arrived at the border at 2 a.m. 

Here is how the petition for cert presents the question in Diaz:

Federal Rule of Evidence 704(b) provides: “In a criminal 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?