The Supreme Court has ruled in a 6-3 decision to uphold the conviction of a California woman, Delilah Guadalupe Diaz, who was found with a stash of methamphetamine hidden inside her car. The majority opinion dismissed arguments that an expert witness for the prosecution had overstepped in describing the woman's mindset, stating that the opinion about most drug couriers did not apply to all couriers.
Justice Clarence Thomas, writing the decision, was joined by Chief Justice John Roberts, Justices Samuel Alito, Brett Kavanaugh, Amy Coney Barrett, and liberal Justice Ketanji Brown Jackson. In a dissenting opinion, Justice Neil Gorsuch expressed concern that the ruling could give the government excessive power by allowing expert witnesses to speculate on a defendant's mental state.
The case stemmed from an incident where Border Patrol agents discovered nearly $370,000 worth of methamphetamine hidden in Diaz's car door panel as she crossed the U.S.-Mexico border. Diaz claimed she was unaware of the drugs, arguing that the car belonged to her boyfriend and that she was a 'blind mule' used by drug cartels to unknowingly transport contraband.
The Justice Department called a Homeland Security agent as an expert witness, who testified that drug cartels typically do not send large quantities of drugs with individuals who are unaware of the contents. Diaz appealed her conviction, citing a rule that expert witnesses should not provide opinions on a defendant's mental state.
The ruling in Diaz v. United States, 23-14, addressed a longstanding legal issue regarding expert testimony on a defendant's mental state, dating back to the trial of John Hinckley Jr. in 1981. The decision has implications for future cases involving expert witnesses and mental state evaluations.
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