Diaz and Gorsuch Dissent

Reuters Legal News

’ Diaz ’ and Gorsuch ’ s dissent : seeking other provisions to bar expert testimony on criminal defendant ’ s mental state

By Nicole Boeckmann , Esq ., and Meagan Maloney , Esq ., Bracewell LLP JULY 10 , 2024
In June 2024 , the United States Supreme Court held that Federal Rule of Evidence 704 ( b ) does not prohibit an expert witness from offering testimony relating to a criminal defendant ’ s mental state , so long as the testimony does not conclusively state whether the defendant did or did not have the requisite mental state to commit a crime . The decision is likely to increase the use and reliance on expert witnesses to establish or refute mens rea in criminal cases .
Aware or not aware ?
Diaz v . United States involved the drug-trafficking prosecution of a defendant who asserted a “ blind mule ” defense , arguing she was unaware of the drugs hidden in her car when she crossed the Southern border into the United States . To secure a conviction , the Government had to prove that Diaz “ knowingly ” transported the drugs into the United States .
It attempted to do so , in part , using an expert witness who would testify that most drug traffickers do not entrust large quantities of drugs to people who are unaware of what they are transporting and that , as such , most couriers are aware that they are transporting drugs .
The decision is likely to increase the use and reliance on expert witnesses to establish or refute mens rea in criminal cases .
Diaz objected to the expert ’ s testimony under Federal Rule of Evidence 704 ( b ), which provides :
” In a criminal case , an expert witness must not state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense . Those matters are for the trier of fact alone .”
According to Diaz , the expert opinion testimony that most drugcouriers know they are transporting drugs was the functional equivalent of an opinion as to whether Diaz herself knew she was transporting drugs , an ultimate issue of fact for the jury . After both the District Court and Court of Appeals ruled against her on this issue , Diaz appealed to the Supreme Court .
Writing for the majority , Justice Clarence Thomas concluded that the expert testimony did not violate Rule 704 ( b ) and affirmed Diaz ’ s conviction .
Writing for the dissent , Justice Neil Gorsuch makes a compelling case for a much broader interpretation of the exception than that adopted by the majority .
Justice Thomas started his analysis with the history of Rule 704 , which departed from the common law “ ultimate issue ” rule . At common law , the “ ultimate issue ” rule barred witness testimony that answered an ultimate issue in the case — one that must be decided by a jury — but allowed witnesses to offer testimony related to an ultimate issue .
The challenge of ‘ ultimate issue ’
Initially designed to prevent witnesses from usurping the jury ’ s role as the ultimate-fact finder , commentators soon realized that in practice , the “ ultimate issue ” rule did not serve its intended purpose . Rule 704 thus abolished the common law rule in federal court and permitted all witness testimony on ultimate issues without exception .
It wasn ’ t until after the acquittal of John Hinckley Jr . for the attempted assassination of President Ronald Reagan — a trial that quickly digressed into a battle of experts concerning Hinckley ’ s mental state — that Congress introduced Rule 704 ( b ).
According to the majority , Rule 704 ( b ) was intended as a “ narrow ” exception to the Rule allowing ultimate issue testimony , which by its terms only bars “ expert opinions in a criminal case that are about a particular person (’ the defendant ’) and a particular ultimate issue ( whether the defendant has ‘ a mental state or condition ’ that is ‘ an element of the crime charged or of a defense ’).”
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