Expert Testimony Admitted Because it Does Not Consist of Opinions on the Defendant’s Mental State
Posted on July 8, 2024 by Expert Witness Profiler
Delilah Diaz was stopped at the U.S.-Mexico border with over 54 pounds of methamphetamine hidden in her vehicle. She was charged with importing methamphetamine and she claimed not to know that the drugs were hidden in the car. To rebut Diaz’s claim, the Government planned to call Homeland Security Investigations Special Agent Andrew Flood as an expert witness to testify that drug traffickers generally do not entrust large quantities of drugs to people who are unaware they are transporting them.
Rule 704(b) provides that “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.”
Discussion by the Court
Federal Rule of Evidence 704(a) sets out a general rule that “an opinion is not objectionable just because it embraces an ultimate issue.”
Rule 704(b) in criminal trials aims to prevent expert witnesses from directly stating their opinions about a Defendant’s mental state. This rule is crucial because it ensures that the jury independently evaluates and decides on the Defendant’s mental state, a central issue in the trial. By maintaining this separation, the rule upholds the jury’s primary responsibility to assess evidence and make determinations regarding the Defendant’s state of mind.
The Court held that Agent Flood’s testimony did not violate Rule 704(b) because Agent Flood did not express an opinion about whether Diaz herself knowingly transported methamphetamine. Instead, he testified about the knowledge of most drug couriers. That opinion does not necessarily describe Diaz’s mental state.
Diaz argued that Agent Flood functionally stated an opinion about whether she knowingly transported drugs when he opined that most couriers know that they are transporting drugs. The Court stated that an opinion about most couriers is not an opinion about all couriers.
Agent Flood asserted that Diaz was part of a group of persons that may or may not have a particular mental state. The ultimate issue of Diaz’s mental state was thus left to the jury’s judgment.
The Court agreed with Diaz that Agent Flood could not testify in absolute terms about whether all couriers knowingly transported drugs. But, insofar as Agent Flood planned to testify only that most couriers know they are transporting drugs, the Court concluded that his testimony was admissible.
Held
Agent Flood’s opinion that “most people” in a group have a particular mental state is not an opinion about “the Defendant” and thus did not violate Rule 704(b). Because Agent Flood did not opine about whether Diaz knowingly transported methamphetamine, the Court concluded that the testimony did not violate Rule 704(b).
Key Takeaway:
Rule 704(b) applies only to opinions about the Defendant. 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.
Case Details:
| Case Caption: | Diaz V. United States |
| Docket Number: | 23-14 |
| Court: | Supreme Court of the United States |
| Order Date: | June 20, 2024 |
