DIAZ v. UNITED STATES
No. 23–14
SUPREME COURT OF THE UNITED STATES
Decided June 20, 2024
602 U. S. 526
Syllabus
DIAZ v. UNITED STATES
CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE NINTH CIRCUIT
No. 23–14. Argued March 19, 2024—Decided June 20, 2024
Petitioner Delilah Diaz was stopped at a port of entry on the United States-Mexico
Held: 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
(a)
(b) In this case, 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. Because Agent Flood did not express an opinion about whether Diaz herself knowingly transported methamphetamine, his testimony did not violate
Diaz‘s counterarguments are unpersuasive. She first argues 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. But 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. Diaz next relies on dictionary definitions of “about” to argue that
Affirmed.
THOMAS, J., delivered the opinion of the Court, in which ROBERTS, C. J., and ALITO, KAVANAUGH, BARRETT, and JACKSON, JJ., joined. JACKSON, J., filed a concurring opinion, post, p. 538. GORSUCH, J., filed a dissenting opinion, in which SOTOMAYOR and KAGAN, JJ., joined, post, p. 542.
Jeffrey L. Fisher argued the cause for petitioner. With him on the briefs were Pamela S. Karlan, Easha Anand, L. Nicole Allan, and Carlton F. Gunn.
Matthew Guarnieri argued the cause for the United States. With him on the brief were Solicitor General Pre-logar, Acting Assistant Attorney General Argentieri, Deputy Solicitor General Feigin, and Javier A. Sinha.*
Opinion of the Court
JUSTICE THOMAS delivered the opinion of the Court.
I
In August 2020, Delilah Diaz, a United States citizen, attempted to enter the United States from Mexico. When Diaz drove into the port of entry, a border patrol officer asked her to roll down the car‘s rear driver-side window. Diaz responded that the window was manual, so the officer left his inspection booth and tried to roll down the window himself. The officer “felt some resistance” and then heard “a crunch-like sound in the door.” App. 25. Aware from experience that car doors are a common hiding spot for con-traband, the officer investigated further with a “buster,” a handheld tool that measures an object‘s density. After the buster detected an abnormal density in the doors, officers brought in a narcotics detection canine and sent the car through an X-ray machine. They discovered 56 packages of methamphetamine tucked inside the car‘s door panels and underneath the carpet in the
Diaz was arrested and, after waiving her Miranda rights, agreed to an interview. See Miranda v. Arizona, 384 U. S. 436 (1966). Diaz claimed that she had no idea drugs were hidden in the car. The officers, however, found her story hard to believe. Diaz explained that she was driving her boyfriend‘s car. Contradictorily, she also told officers that she had seen her boyfriend only “two, three times tops,” did not know his phone number, and did not know where he lived. Response in Opposition in No. 3:20–cr–02546 (SD Cal.), ECF Doc. 33–1, p. 13. Diaz‘s story grew even more dubious when officers questioned her about two cellphones discovered inside the car. She acknowledged that she owned one of the phones. But, she maintained the other phone had been “given to [her]” by a friend—whom she would “rather not” identify. Id., at 32, 34. And, she insisted that the phone was “locked” and that she did not “have access to it.” Id., at 32–33.1
Diaz was charged with importing methamphetamine in violation of
Diaz objected to Agent Flood‘s proffered testimony under
At trial, Agent Flood testified that “in most circumstances, the driver knows they are hired . . . to take the drugs from point A to point B.” App. to Pet. for Cert. 15a. To use an unknowing courier, Agent Flood explained, would expose the drug-trafficking organization to substantial risk. The organization could not guarantee where, if at all, the drugs would arrive. Id., at 16a, 26a. Even if the drugs reached the intended destination, the organization would then have to retrieve the drugs without detection. Id., at 16a, 24a–25a. According to Agent Flood, drug-trafficking organizations are often unwilling to take those chances with hundreds of thousands of dollars on the line. Agent Flood acknowledged on cross-examination that drug-trafficking
The jury found Diaz guilty, and the District Court sentenced her to 84 months’ imprisonment. On appeal, Diaz again challenged Agent Flood‘s testimony under
We granted certiorari, 601 U. S. ––– (2023), and now affirm.
II
“EXCEPTION: 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.”
The logic underpinning the ultimate-issue rule was that it prevented witnesses from taking over the jury‘s role. See 1 K. Broun, McCormick on Evidence 80 (7th ed. 2013) (McCormick) (explaining that the rule‘s “stated justification” was to exclude testimony that “usurps the function” or “invades the province of the jury” (internal quotation marks and footnote omitted)). If a witness gave an opinion “covering the very question which was to be settled by the jury,” some feared that the jury would be left with “no other duty but that of recording the finding of [[the]] witnes[[s]].” Chicago & Alton R. Co. v. Springfield & N. W. R. Co., 67 Ill. 142, 145 (1873).
About nine years later, in the wake of the John Hinckley, Jr., trial, Congress created the exception now found in
By its terms,
III
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.” App. to Pet. for Cert. 15a. That opinion
her counsel described it, the boyfriend then loaned Diaz a car that was secretly loaded with drugs for her drive back to the United States. Diaz supported that story during her case in chief. She presented an automobile mechanics expert who testified that there was “no way for someone to suspect or know that there was drugs hidden within th[[e]] car.” Trial Tr., ECF Doc. 113, p. 62. Diaz also challenged the Government‘s contrary theory. On cross-examination, Diaz‘s counsel highlighted that Agent Flood was not involved in Diaz‘s case and that the Government itself was aware of cases involving unknowing couriers.
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
Diaz‘s counterarguments, echoed by the dissent, are not persuasive. Diaz and the dissent argue that Agent Flood “functional[[ly]]” stated an opinion about whether Diaz knowingly transported drugs when he opined that couriers generally transport drugs knowingly. Brief for Petitioner 24 (internal quotation marks omitted); see also post, at 549 (opinion of GORSUCH, J.). That argument mistakenly conflates an opinion about most couriers with one about all couriers. A hypothetical helps explain why this distinction matters under
Here, by contrast, Agent Flood asserted that Diaz was part of a group of persons that may or may not have a particular mental state. Of all drug couriers—a group that includes Diaz—he opined that the majority knowingly transport drugs. The jury
Diaz and the dissent next zero in on the word “about” in
The reading offered by Diaz and the dissent would have the exception swallow the rule. If
IV
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
It is so ordered.
DIAZ v. UNITED STATES
No. 23–14
SUPREME COURT OF THE UNITED STATES
Decided June 20, 2024
602 U. S. 526
JACKSON, J.
I join the Court‘s opinion in full.
I write separately to emphasize that, as Congress designed it,
I
This very case illustrates the significance of mental-state evidence to both parties in a criminal trial. The Government expert opined (based on his almost 30 years of experience as a special agent) that, “in most circumstances,” drug couriers know that they are transporting drugs. App. to Pet. for Cert. 10a, 15a. Diaz challenged this testimony, and, today, the Court holds that the Government did not violate
For the reasons described in today‘s opinion, none of that evidence would deprive the jury of its ability to decide the last link in the inferential chain: whether Diaz herself had the requisite mens rea. But, at the same time, having all of
this testimony might have helped the jury determine whether the Government had
Other examples provide further proof. Consider expert evidence on mental health conditions. Congress crafted
Or consider defendants who have been subject to domestic abuse. “A number of myths and misconceptions about [[battered woman syndrome]] victims affect our criminal justice system,” and it is clear that those mistaken views “affect jurors.” Linn v. State, 929 N. W. 2d 717, 742 (Iowa 2019); see also id., at 742–746 (summarizing relevant evidence).
II
All that said, I fully acknowledge that there are serious and well-known risks of overreliance on expert testimony—risks that are especially acute in criminal trials. See NAFD Brief 21–22, 24–25; see also United States v. Alvarez, 837 F. 2d 1024, 1030 (CA11 1988) (“When the expert is a government law enforcement agent testifying on behalf of the prosecution about participation in prior and similar cases, the possibility that the jury will give undue weight to the expert‘s testimony is greatly increased”). But there are also safeguards outside of
This means, of course, that when faced with flawed or faulty testimony concerning
District court judges also have a role to play. They should be protective of Congress‘s intent to preserve the jury‘s core duty, by providing specific admonitions and instructions when expert testimony about a relevant mental state is introduced. See Evidence Professors Brief 27–29; see also United States v. Smart, 98 F. 3d 1379, 1388–1389 (CADC 1996) (requiring that district courts sometimes use jury instructions to prevent expert testimony from violating
With this understanding of both the important uses and the potential misuses of
DIAZ v. UNITED STATES
No. 23–14
SUPREME COURT OF THE UNITED STATES
Decided June 20, 2024
602 U. S. 526
GORSUCH, J.
JUSTICE GORSUCH, with whom JUSTICE SOTOMAYOR and JUSTICE KAGAN join, dissenting.
I
Delilah Diaz‘s conviction for drug trafficking turned on her state of mind. In that, hers was an everyday case. Often in our criminal justice system, the difference between freedom and years in prison turns on just that question. Perhaps it has always been so. The government‘s duty to prove that the defendant it seeks to convict had a culpable state of mind when committing a proscribed act is as ancient as it is fundamental to our system of justice. At common law, “a complete crime” generally required “both a will” (or mens rea) “and an act” (or actus reus). 4 W. Blackstone, Commentaries on the Laws of England 21 (1769) (Blackstone). That same
Why does our law generally insist not just on a bad act but also a culpable state of mind? A significant part of it has to do with respect for the individual and his liberty in a free society. “Criminal liability imports a condemnation, the gravest we,” as a Nation, “permit ourselves to make.” H. Wechsler, American Law Institute II–A Thoughtful Code of Substantive Law, 45 J. Crim. L. & C. 524, 528 (1955) (Wechsler); see also 4 Blackstone 20–21; 1 Bishop § 287, at 161. Of course, our law recognizes gradations of mens rea, ranging from purpose and knowledge to recklessness and negligence. See, e. g.,
At trial, deciding whether a criminal defendant acted with a culpable mental state is a job for the jury. No matter how “clear the proof” or “incontrovertible” the inference, the question whether a defendant possessed a culpable mens rea “must always be submitted to the jury.” Id., at 274 (internal quotation marks omitted). Always, too, the government bears the burden of proving the requisite mens rea. Never, we have held, may the government seek to “shift the burden of proof to the defendant.” Patterson v. New York, 432 U. S. 197, 215 (1977); see Mullaney v. Wilbur, 421 U. S. 684 (1975). Nor may a court instruct a jury that it must presume a defendant‘s state of mind from any particular set of facts, no matter how compelling they may be. Francis v. Franklin, 471 U. S. 307, 316 (1985).
Reflecting the centrality of mens rea to criminal punishment and the jury‘s role in finding it,
Gorsuch, J., dissenting
eral Rules of Evidence 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 the crime charged or of a defense.” As the Rule continues: “Those matters are for the trier of fact alone.”
By all accounts, the immediate impetus for the Rule was the trial of John Hinckley for the attempted assassination of President Ronald Reagan. Ante, at 533. In that case, experts didn‘t just offer competing views on whether Hinckley suffered from a medically diagnosable mental illness. They went much further. The trial descended into a battle between experts who claimed to know exactly what Hinckley was (or was
In the trial‘s aftermath, Congress continued to recognize the value of expert mental health evidence. So, for example, an expert may still testify that the defendant suffered from some diagnosable illness or syndrome at the time of the charged act and discuss its symptoms. Cf. ante, at 540-541 (Jackson, J., concurring) (discussing schizophrenia and battered woman syndrome). From testimony like that, a jury might infer that the defendant did not have the requisite mental state to convict. But in
II
The government violated that Rule in this case. Proceedings began when prosecutors charged Ms. Diaz with importing a controlled substance into this country. See
To help prove that Ms. Diaz “knowingly” imported drugs, the government called to the stand Andrew Flood, one of its own employees, an agent with the Department of Homeland Security. Ms. Diaz had made no admissions to him about her mental state, nor had Agent Flood even interviewed her. Instead, prosecutors called Agent Flood as an expert on the minds of drug couriers (yes, really). App. 17; United States’ Notice in No. 3:20-cr-02546 (SD Cal.), ECF Doc. 30, p. 7. And in response to the government‘s questions, Agent Flood testified that, “in most circumstances, the driver knows they are hired . . . to take the drugs from point A to point B.” App. to Pet. for Cert. 15a.
That was a violation of
To be sure, prosecutors thought they had a clever way around the problem. They did not ask Agent Flood to testify explicitly about Ms. Diaz‘s mental state. Instead, they asked the agent to testify about the mental state of people exactly like Ms. Diaz, drivers bringing drugs into the country. And that, the prosecutors argued, made all the difference. See App. 32a; Brief for United States in No. 21-50238 (CA9), pp. 46, 58. The Ninth Circuit endorsed the government‘s maneuver, holding that
Before us, however, even the government disavows the full implications of that reasoning. Now, it concedes, the Rule does more than bar an expert from testifying “explicitly” that the defendant had the mental state required for conviction. Tr. of Oral Arg. 72-73, 76. The Rule also bars an expert from testifying that a class of persons (say, all people carrying drugs over the border) has the legally proscribed mental state when that class includes the defendant. Brief for United States 36; ante, at 535-536. Likewise, the Rule bars an expert from opining that a hypothetical person who matches the defendant‘s description (say, a hypothetical woman who drives a car full of drugs across the border) will have the mental state required for conviction. Tr. of Oral Arg. 67. All those opinions, the government now acknowledges, are “about” the defendant‘s mental state and cannot be offered consistent with
III
So what is left? Instead of vacating and remanding the case to the Ninth Circuit to correct its error, the government asks us to affirm its judgment on other grounds. As the government sees it, Agent Flood‘s opinion was permissible for a different reason than the Ninth Circuit offered. It was permissible, the government says, because it wasn‘t definitive. So, yes, an expert cannot testify that all persons in a class that includes the defendant have a culpable mental state. Brief for United States 36. But, the government insists, everything changes when an expert offers (as Agent Flood offered) only a probabilistic assessment that most such persons do.
I cannot see how that gambit begins to solve the government‘s problem. The Rule does not only prohibit an expert from stating a definitive opinion about the defendant‘s mental state (or, as the government concedes, the mental state of a class that includes her). It prohibits an expert from offering any opinion on the subject. Return, once more, to the Rule‘s terms. It bars an expert from stating an opinion ”about whether the defendant” had “a mental state . . . that constitutes an element of the crime charged.” (Emphasis added.) The word “about” means “[c]oncerning, regarding, with regard to, in reference to; in the matter of.” Oxford English Dictionary (3d ed., June 2024); see Brief for Petitioner 18; see also American Heritage Dictionary 5 (def. 4a) (5th ed. 2011). So whether an expert‘s opinion happens to be definitive or probabilistic makes no difference. An expert may not state any opinion concerning, regarding, or in reference to whether the defendant, while committing a charged criminal act, had the requisite mental state to convict. Period. Lest any doubt remain, the Rule takes pains to emphasize, “[t]hose matters are for the trier of fact alone.”
Observe, as well, where today‘s tiptoeing around the Rule promises to lead. The Court adopts the government‘s muddled view that an expert cannot offer a probabilistic opinion about the mental state of the defendant explicitly but can offer a probabilistic opinion about the mental state of a group that includes the defendant. So what happens next? In this case, Agent Flood said “most” people in the defendant‘s shoes have the requisite mens rea. But what if he said, as the government initially proffered, that drivers “generally” know? ECF Doc. 30, at 7. Or that they “almost always” know? Or perhaps an expert puts a finer point on it: “In my experience, 99% of drug couriers know.” When cases like those come to us, likely one of two things will happen. We will draw some as-yet unknown line and say an expert‘s probabilistic testimony went too far. Or we will hold anything goes and eviscerate
IV
The government‘s approach, adopted by the Court today, is no more necessary than it is appropriate. Yes, proving a defendant‘s mental state at trial can require work. Normally, it will require the government to resort to circumstantial evidence and inference. After all, defendants in life do not confess their inner thoughts on the stand nearly as often as they do in courtroom dramas. But there is nothing new about any of that. See 4 Blackstone 21 (“no temporal tribunal can search the heart, or fathom the intentions of the mind, otherwise than as they are demonstrated by outward actions“). Nor is it any secret that the government has a long track record of success in proving mens rea the old-fashioned way by presenting circumstantial evidence and appealing to reasonable inferences.
This case illustrates how it can be—and regularly is—done. To persuade the jury that Ms. Diaz knew about the drugs, the government could point to the amounts involved—54 pounds of drugs worth over $360,000. Ante, at 529. It could also point to the holes in her story. She claimed the car was her boyfriend‘s, but then said she had met him only “three times tops,” did not know his phone number, and did not know where he lived. ECF Doc. 33-1, at 13, 32. The government could point out, too, that when cell phones were found in the car, Ms. Diaz maintained one of them belonged to a friend, someone she would “rather not” identify. Id., at 34. As well, the government could highlight her statement that the phone was “locked” and she did not “have access to it.” Id., at 32-33. And the government could then ask a jury to infer from all these facts that Ms.
To the contrary, there are sound reasons why
The particular nook of the criminal law we find ourselves in today illustrates the soundness of Congress‘s approach. Not long ago, the government tried—often successfully—to put “experts” (really, like Agent Flood, its own law enforcement agents) on the stand to testify that all couriers know when they are carrying drugs. See, e. g., United States v. Flores, 510 Fed. Appx. 594, 595 (CA9 2013). Not only was that testimony improper under the government‘s own current understanding of
None of this serves our criminal justice system well. A criminal conviction is “the gravest” condemnation we as a society “permit ourselves to make.” Wechsler 528. Allowing into our proceedings speculative guesswork about a defendant‘s state of mind diminishes the seriousness due them. It risks the reliability of the outcomes they produce (just ask those convicted in cases where government experts opined that “all” couriers know). It undermines our historic commitment that mens rea is a necessary component of every serious crime by turning the inquiry into a defendant‘s mental state from an exacting one guided by hard facts and reasonable inferences into a competing game of “I say so.” It diminishes our respect for the presumptively free person, his free will and individuality, by encouraging the lazy assumption that he thinks like “most.” And it reduces the vital role juries are meant to play in criminal trials. Yes, they can still decide whether the defendant thinks like “most” people. Ante, at 535. But that role hardly matches
In describing what I see as some of the possible consequences of the government‘s approach adopted by the Court today, I do not mean to suggest they are inevitable. Today‘s decision may go a long way toward hollowing out
Take a few examples. Under
Meanwhile, the danger of unfair prejudice can run very high. It can be “difficult for the individual to make his own case stand on its own merits in the minds of the juror[s]” when jurors are told by an expert “that birds of a feather are flocked together.” Krulewitch v. United States, 336 U.S. 440, 454 (1949) (Jackson, J., concurring). As this Court has recognized, too, expert opinions about the defendant‘s “state of mind at the crucial moment” when committing a criminal act may “easily mislead” the jury into “thinking the opinions show more than they do.” Clark v. Arizona, 548 U.S. 735, 776 (2006). Even the government candidly admits
The risk of unfair prejudice can be exacerbated, too, where, as here, the professed expert “carries with [him] the imprimatur of the [g]overnment.” United States v. Young, 470 U.S. 1, 18 (1985). A witness like that “may induce the jury to trust [the witness‘s] judgment rather than its own view of the evidence.” Id., at 18-19; see also United States v. Scheffer, 523 U.S. 303, 314 (1998) (plurality opinion) (experts like these may attain an “aura of infallibility“). For precisely that reason, the government
Add to those Rules at least one more. As part of its “gatekeeping” functions, a federal court must ensure that any expert testimony it permits is reliable, grounded on widely accepted principles, and will “`assist the trier of fact to understand the evidence.‘” Kumho Tire Co, 526 U.S., at 147 (quoting
Nor does testimony like that help the jury understand “`experience[s] confessedly foreign in kind to [its] own.‘” Kumho Tire Co., 526 U.S., at 149 (quoting L. Hand, Historical and Practical Considerations Regarding Expert Testimony, 15 Harv. L. Rev. 40, 54 (1901)). In a criminal trial, expert testimony about DNA testing or the chemical composition of illegal drugs may sometimes help a jury understand facts they do not encounter in daily life. But none of that holds true when it comes to the job of assessing whether a defendant‘s story about her state of mind is credible or (as the government puts it) “transparently flimsy.” Brief in Opposition 16. Jurors are more than up to performing that task, and they hardly need the help of some clairvoyant.
*
Persuaded that today‘s decision is mistaken, but hopeful that it will ultimately prove immaterial in practice, I respectfully dissent.
Reporter‘s Note
The attached opinion has been revised to reflect the usual publication and citation style of the United States Reports. The revised pagination makes available the official United States Reports citation in advance of publication. The syllabus has been prepared by the Reporter of Decisions for the convenience of the reader and constitutes no part of the opinion of the Court. A list of counsel who argued or filed briefs in this case, and who were members of the bar of this Court at the time this case was argued, has been inserted following the syllabus. Other revisions may include adjustments to formatting, captions, citation form, and any errant punctuation. The following additional edits were made:
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