Published on: Thursday, August 24, 2023

Law enforcement agents sometimes find unlawul drugs concealed in vehicles attempting to cross into the United States from Mexico. The drivers of these vehicles commonly deny knowledge of the drugs, arguing they are unknowing couriers, aka "blind mules."  Of course, in a prosecution for importation of illegal drugs, the government must prove that the defendant knew she was transporting drugs in order to separate wrongful conduct from innocent conduct. Proving the knowledge element has led to a circuit split: 

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?

Diaz v. United States, No. 23-14 (U.S. June 30, 2023) (cert. petition filed). Delilah Diaz's pending p-cert is available here. Petitioner Diaz was apprehended on the Southern Border after investigators found methamphetamine hidden in the door panels of the car she was driving. To counter Diaz's blind mule defense at trial, the government called a Homeland Security agent to testify in an expert capacity that “in most circumstances, the driver knows they are hired” to transport drugs and that drug-trafficking organizations do not entrust large quantities of drugs to unknowing drivers. Diaz objected and argued this testimony violated FRE 704(b), which prohibits an expert witness in a criminal case from “stat[ing] an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged. The district court and Ninth Circuit disagreed, ruling that expert testimony implicates that rule only when it provides “an ‘explicit opinion’ on the defendant’s state of mind.” 

The agent's testimony in Diaz would have been barred in the Fifth Circuit, which has repeatedly held that Rule 704(b) prohibits not just “explicit opinions” on mental state but also “the ‘functional equivalent’ of a prohibited opinion on mental state.” United States v. Gutierrez-Farias, 294 F.3d 657, 663 (5th Cir. 2002). The Eighth and Eleventh Circuit's agree with the Ninth Circuit in permitting expert testimony that most couriers know they are carrying drugs. See, e.g., United States v. Urbina, 431 F.3d 305, 311-12 (8th Cir. 2005); United States v. Alvarez, 837 F.2d 1024, 1031 (11th Cir. 1988); United States v. Russell, 799 F. App’x 747, 750-51 (11th Cir. 2020).

The Training Division provides Blind Mule Resources here demonstrating that, in recent years, the government has acknowledged that the use of "blind mules" to smuggle drugs is, in fact, widespread.