Supreme Court Clarifies Expert Testimony Rule in Drug Case (1)

The US Supreme Court clarified a rule on expert witness testimony that prohibits them from giving an opinion on a defendant’s state of mind.

In a 6-3 ruling by Justice Clarence Thomas on Thursday weighing in on the question of criminal intent or mens rea, the court said expert witnesses can testify on what most defendants would typically know when an offense was being committed.

The decision that crossed ideological lines agreed with prosecutors that their expert witness didn’t go too far when telling a jury that drug dealers typically don’t entrust large quantities of narcotics to “blind mules.” Those are people who unwittingly traffic drugs.

Testimony about what most people know, as opposed to what all people know, doesn’t violate Federal Rule of Evidence 704(b), the court said in upholding Delilah Guadalupe Diaz’s conviction for attempting to smuggle more than $350,000 worth of methamphetamine across the US-Mexico border.

A dissent written by Justice Neil Gorsuch called the court’s distinction between what most or all people know a “charade,” and said the question of what a defendant knows is one for the jury alone.

“Jurors are more than up to performing that task, and they hardly need the help of some clairvoyant,” Gorsuch said.

Ultimate Issue

The rule limiting expert witnesses testimony was a reaction to the acquittal of would-be presidential assassin John Hinckley Jr.

Hinckley, who shot and wounded President Ronald Reagan in 1981 in Washington, was found not guilty by reason of insanity after dueling experts testified about his mental state.

Congress responded with an exception to the general rule that experts can provide an opinion about the “ultimate issue,” which in the newly decided case involves mental state.

Emphasizing that the exception was “narrow,” the court said that “Rule 704(b) applies only to opinions about the defendant.” Because the expert in the drug smuggling case “did not express an opinion about whether Diaz herself knowingly transported methamphetamine, his testimony did not violate” that rule.

Justice Ketanji Brown Jackson broke with her liberal colleagues in agreeing that the testimony passed muster. But she wrote separately to emphasize that the rule is “party agnostic.”

The “type of mental-state evidence that Rule 704(b) permits can prove essential not only for prosecutors, but for defendants as well,” Jackson wrote.

‘Junk Science’

Gorsuch’s dissent, joined by Justices Sonia Sotomayor and Elena Kagan, was dismissive of the evidence offered at Diaz’s trial. Prosecutors called a federal agent “as an expert on the minds of drug couriers (yes, really),” Gorsuch wrote.

He warned that the “problem of junk science in the courtroom is real and well documented.” Perhaps “no ‘science’ is more junky than mental telepathy,” he said.

In addition to calling into question the validity of the evidence, Gorsuch said allowing its use usurps the jury’s role to determine the defendant’s state of mind. “On that particular issue, Congress has concluded that jurors need no help from experts,” Gorsuch wrote.

The case is Diaz v. United States, U.S., No. 23-14.