SCOTUS Rules Against Convicted Drug 'Mule' in Testimony Dispute

The U.S. Supreme Court on Thursday ruled against a California woman convicted of smuggling drugs across the U.S.-Mexican border who challenged prosecution expert testimony that cast doubt on her claim that she acted unwittingly as a "blind" drug mule.

The justices, in a 6-3 ruling, upheld a lower court's decision to allow testimony by an expert witness who called into question Delilah Guadalupe Diaz's contention that she did not know that methamphetamine valued at $368,550 was hidden in the door panels of the car she was driving.

The case tested how far law enforcement agents appearing in trials as expert witnesses can go in telling a jury that defendants in certain drug trafficking cases generally have a "guilty mind." A judge in this case allowed an expert witness to testify in the trial that drivers usually know they are being hired to traffic drugs.

A jury in federal court in San Diego found Diaz guilty in 2021 of illegally importing the methamphetamine, a crime that required proving that she knew the drugs were in the car. Diaz was sentenced to seven years in prison.

Diaz's lawyers argued that the testimony violated a provision of the longstanding Federal Rules of Evidence governing the types of evidence allowable in legal cases. The rule bars expert witnesses from opining on the "mental state" of defendants related to an alleged offense and whether they knew they were committing a crime.

U.S. District Judge Anthony Battaglia during the trial let the prosecution's expert witness, a Homeland Security special agent, testify that "in most circumstances, the driver knows they are hired." The expert also told the jury that drug-trafficking organizations generally do not entrust large quantities of drugs to unknowing couriers.

People who smuggle drugs across borders, sometimes called "mules," may do so for profit but also sometimes do it unwittingly, transporting illegal substances that were planted on them. These individuals are often called "blind" mules.

In 2020, border inspectors ordered Diaz, a resident of Moreno Valley, California, to roll down a window of the Ford Focus vehicle she was driving and heard a "crunch-like" sound, later finding 56 packages containing more than 24 kilograms of pure methamphetamine. Diaz denied knowledge of the drugs.

She carried two cellphones — one locked that she could not open — and claimed that the car belonged to a boyfriend she had visited in Mexico whose phone number and residence she could not identify. The car also had a hidden GPS device.

The Supreme Court heard arguments in the case in March.