The Supreme Court agreed to wade into a dispute in jurisdictions adjacent to international borders on when expert witnesses can testify in drug trafficking cases in which the defendants say they were "blind mules" (or unknowing transporters of drugs).

The case known as Diaz v. United States involves California resident Delilah Diaz, who was sentenced to 84 months in prison after she was discovered with $368,550 worth of methamphetamine carefully stuffed into the crevices of her vehicle at the southern border. Diaz contends she didn't know there were drugs in her car and said she was using a vehicle that belonged to her boyfriend.

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"The type of expert testimony at issue in this case — that is, expert testimony that most people caught with drugs know they are transporting drugs and that drug-trafficking organizations rarely entrust large quantities of drugs to blind mules — can make the difference between a verdict of acquittal and a hefty mandatory minimum sentence," Diaz's attorneys argue.

Justices will consider Federal Rule of Evidence 704(b), which blocks expert witnesses in criminal cases from stating an opinion about whether a defendant had a "mental state or condition that constitutes an element of the crime charged."

The 9th U.S. Circuit Court of Appeals affirmed Diaz's conviction, holding that the federal rule only excludes expert witnesses from stating an express opinion about whether a specific person knew they were engaging in criminal activity, not from making general observations about similar defendants and the likelihood of their liability for the alleged crimes.

"The Government nevertheless charged her with importing methamphetamine in violation of 21 U.S.C. §§ 952 and 960 — a crime that requires proof that the defendant knew she was transporting illegal drugs," her attorneys wrote in their Supreme Court petition.

Her attorneys also contended the case was necessary for the justices' consideration due to conflicting rulings in the 9th and 5th U.S. Circuit Courts of Appeals.

Justice Department Solicitor General Elizabeth Prelogar replied to Diaz's brief on Sept. 28, arguing her "flimsy story" provided a "specific and convincing basis for the jury to find beyond a reasonable doubt that petitioner knew that she was carrying the methamphetamine."

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"It accordingly would have made such a finding with or without [a special agent's] more generalized testimony about drug-courier practices," Prelogar added.

A date has not been selected for oral arguments, but the Supreme Court will likely weigh it next year before the end of May.