Supreme Court Decision Syllabus (scotus)

 Petitioner Delilah Diaz was stopped at a port of entry on the United States-Mexico border. Border patrol officers searched the car that Diaz was driving and found more than 54 pounds of methamphetamine hidden in the vehicle. Diaz was charged with importing methamphetamine in violation of 21 U. S. C. §§952 and 960, charges that required the Government to prove that Diaz “knowingly” transported drugs. In her defense, Diaz 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. Diaz objected in a pretrial motion under Federal Rule of Evidence 704(b), which provides that “[i]n 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