Diaz v. United States
View Official PDFBelow are plain-language sections to help you understand what the Court decided in Diaz v. United States and why it matters. Quotes are taken from the syllabus (the Court’s short summary at the start of the opinion).
Summary
A short, plain-English overview of Diaz v. United States.
In Diaz v. United States, the Supreme Court reviewed whether expert testimony violated Federal Rule of Evidence 704(b) in a case where Delilah Diaz was charged with drug importation. The government used testimony from an expert witness who stated that most drug couriers know they are transporting drugs. The Ninth Circuit upheld the testimony, and the Supreme Court affirmed, ruling that the testimony did not violate Rule 704(b) as it did not directly address Diaz's mental state.
Holding
The single most important “bottom line” of what the Court decided in Diaz v. United States.
The Court held that expert testimony stating that 'most people' in a group have a particular mental state does not violate Rule 704(b) as it does not directly address the defendant's mental state.
Constitutional Concepts
These are the Constitution-related themes that appear in Diaz v. United States. Click a concept to see other cases that involve the same idea.
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Why Due Process is relevant to Diaz v. United States
The case involves the interpretation of Federal Rule of Evidence 704(b) and its application in ensuring fair trial procedures, which is a component of procedural due process.
Syllabus excerpt (verbatim)Diaz appealed, challenging Agent Flood's testimony under Rule 704(b).
Key Quotes
Short excerpts from the syllabus in Diaz v. United States that support the summary and concepts above.
Expert testimony 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).
Rule 704(b) addresses only conclusions as to the defendant's mental state.
Because Rule 704(b) is an 'exception' to Rule 704(a), Rule 704(b) can only be understood to cover a subset of the testimony that Rule 704(a) expressly allows.