In Diaz v. United States, 602 U.S. ___ (2024), a divided Supreme Court affirmed Diaz's drug-smuggling conviction.
At trial, the Government’s expert witness opined that most drug couriers know that they are transporting drugs.
The majority held that because the expert witness did not state an opinion about whether Diaz herself had a particular mental state, the testimony did not violate Rule 704(b).
Because Agent Flood did not express an opinion about whether Diaz herself knowingly transported methamphetamine, his testimony did not violate Rule 704(b). Agent Flood instead testified about the knowledge of most drug couriers. Specifically, he explained that “in most circumstances, the driver knows they are hired . . . to take the drugs from point A to point B.” That opinion does not necessarily describe Diaz’s mental state. After all, Diaz may or may not be like most drug couriers. Diaz herself made this point at trial. She argued that another person, an alleged boyfriend, had deceived her into carrying the drugs.The jury was thus well aware that unknowing couriers exist and that there was evidence to suggest Diaz could be one of them. It simply concluded that the evidence as a whole pointed to a different conclusion: that Diaz knowingly transported the drugs. The jury alone drew that conclusion. While Agent Flood provided evidence to support one theory, his testimony was just that—evidence for the jury to consider or reject when deciding whether Diaz in fact knew about the drugs in her car. Because Agent Flood did not give an opinion “about whether” Diaz herself “did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense,” his testimony did not violate Rule 704(b).An expert’s conclusion that “most people” in a group have a particular mental state is not an opinion about “the defendant” and thus does not violate Rule 704(b). Accordingly, the judgment of the Court of Appeals is affirmed.
Here is the start of Justice Gorsuch's dissent:
Federal Rule of Evidence 704(b) prohibits an expert witness from offering an opinion “about whether the defendant did or did not have [the] mental state” needed to convict her of a crime. “Those matters,” the Rule instructs, “are for the trier of fact alone.” Following the government’s lead, the Court today carves a new path around that command. There’s no Rule 704(b) problem, the Court holds, as long as the government’s expert limits himself to testifying that most people like the defendant have the mental state required to secure a conviction.The upshot? The government comes away with a powerful new tool in its pocket. Prosecutors can now put an expert on the stand—someone who apparently has the convenient ability to read minds—and let him hold forth on what “most” people like the defendant think when they commit a legally proscribed act. Then, the government need do no more than urge the jury to find that the defendant is like “most” people and convict. What authority exists for allowing that kind of charade in federal criminal trials is anybody’s guess, but certainly it cannot be found in Rule 704.
