SUPREME COURT OF THE UNITED STATES
_________________
No. 23–14
_________________
DELILAH GUADALUPE DIAZ, PETITIONER
v.
UNITED STATES
on writ of certiorari to the united states
court of appeals for the ninth circuit
[June 20, 2024]
Justice Gorsuch, with whom Justice Sotomayor
and Justice Kagan join, dissenting.
Federal Rule of Evidence 704(b) prohibits an
expert witness from offering an opinion “about whether the
defendant did or did not have [the] mental state” needed to convict
her of a crime. “Those matters,” the Rule instructs, “are for the
trier of fact alone.” Following the government’s lead, the Court
today carves a new path around that command. There’s no Rule 704(b)
problem, the Court holds, as long as the government’s expert limits
himself to testifying that
most people like the defendant
have the mental state required to secure a conviction.
The upshot? The government comes away with a
powerful new tool in its pocket. Prosecutors can now put an expert
on the stand—someone who apparently has the convenient ability to
read minds—and let him hold forth on what “most” people like the
defendant think when they commit a legally proscribed act. Then,
the government need do no more than urge the jury to find that the
defendant is like “most” people and convict. What authority exists
for allowing that kind of charade in federal criminal trials is
anybody’s guess, but certainly it cannot be found in Rule 704.
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 view “took deep and early
root in American soil” where, to this day, a crime ordinarily
arises “only from concurrence of an evil-meaning mind with an
evil-doing hand.”
Morissette v.
United States,
342 U.S.
246, 251–252 (1952); see 1 J. Bishop, Commentaries on the
Criminal Law §291, p. 163 (6th ed. 1877) (Bishop). So ingrained is
this view that courts have long presumed criminal statutes demand
proof of
mens rea even when they are “silent” on the
subject.
Morissette, 342 U. S., at 252; see
Staples v.
United States,
511
U.S. 600, 605 (1994).
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., ALI, Model Penal
Code §2.02 (1985);
United States v.
Bailey,
444 U.S.
394, 404 (1980). But to subject a presumptively free individual
to serious punishments for acts undertaken without proof of any of
that would be “the badge of tyranny, the plainest illustration of
injustice.” Wechsler 528
. The principle “that an injury can
amount to a crime only when inflicted” with some accompanying
mens rea is, we have said, “as universal and persistent in
mature systems of law as belief in freedom of the human will and a
consequent ability and duty of the normal individual to choose
between good and evil.”
Morissette, 342 U. S., at
250.
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, Rule 704(b)
of the Federal 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 6. 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 not) thinking at
the moment he pulled the trigger.
Ibid.
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 3–4
(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 Rule 704(b) Congress declared that task belonged to the jury
alone, and allowing a parade of witnesses to speculate about what
did or did not transpire in the head of a particular defendant at a
particular moment in the past did not reflect well on federal
judicial proceedings and did not aid the jury.
Rule 704(b) may have been a new addition to the
Federal Rules of Evidence, but it reflects a much older tradition.
For centuries, courts have grappled with the role expert witnesses
should play at trial. See,
e.g., 1 S. Greenleaf, Evidence
§440, p. 489 (1842);
Folkes v.
Chadd, 3 Dougl. 157,
158–159, 99 Eng. Rep. 589, 590 (K. B. 1782). For a long stretch,
many courts barred experts from offering opinions on so-called
ultimate issues like
mens rea. See 3 J. Wigmore, Evidence
§§1920, 1921 (1904);
United States v.
Spaulding,
293 U.S.
498, 506 (1935). The Federal Rules of Evidence are no longer so
strict, see Fed. Rule Evid. 704(a), except in one respect:
mens
rea. On that particular issue, Congress has concluded that
jurors need no help from experts. They are fully capable of drawing
reasonable inferences from the facts and deciding whether the
defendant acted with the requisite
mens rea. And in criminal
trials that is their job alone.
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 21
U. S. C. §§952, 960(a)(1). At the trial that followed,
Ms. Diaz did not dispute that she had transported drugs across the
border. The only question concerned her
mens rea. If, as the
government charged, she transported the drugs “knowingly,” she
faced a potential sentence of up to life in prison. See
§§960(a)(1), (b)(1)(H). If, however, Ms. Diaz acted with some
lesser
mens rea (say, negligence), or perhaps innocently (as
what some call a “blind mule”), she was entitled to an
acquittal.
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; 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 Rule 704(b), plain as
day. Just walk through its terms. The government called Agent Flood
as an “expert witness” to address the question “whether the
defendant did or did not have . . . a mental state
. . . that constitutes an element of the crime charged.”
After all, whether Ms. Diaz acted “knowingly” was the only question
at trial, all that separated her from a conviction. And Agent Flood
proceeded to do just as he was asked, offering an “opinion about”
that very question.
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 Rule
704(b) prohibits only testimony “ ‘explicit[ly]’ ” about
the defendant’s mental state, not testimony about the mental state
of a class of persons that includes her. App. to Pet. for Cert. 6a
(quoting
United States v.
Gomez, 725 F.3d 1121, 1128
(2013)).
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 9.
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 Rule
704(b). On this, the Court, too, agrees.
Ante, at 9.
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.”
Consider, too, how the government’s present
theory collapses into the one it has disavowed. Just imagine if
Agent Flood had explicitly addressed Ms. Diaz and said she “most
likely knew” she was carrying drugs. Would that testimony be
permissible under Rule 704(b)? Of course not. Probabilistic though
the testimony may be, an expert who says that an individual
defendant “most likely” had the requisite mental state for
conviction offers an opinion about, concerning, regarding, or in
reference to her mental state. On that, no dispute exists. So how
can it be, as the government insists, that an expert may offer the
probabilistic assessment that “most” people like the defendant know
they are carrying drugs? The only difference between the two
opinions is that the first addresses the defendant “explicitly,”
the second a class that includes her. All of which returns us to a
distinction that the government itself seems to acknowledge the
Rule does not tolerate.
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 Rule 704(b) in the process. Rather than face either
of those prospects, how much easier it would be to follow where the
Rule’s text leads.
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 2. 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. Diaz knew exactly what
she was doing. As it argues to us, the government was free to argue
to a jury, asking it to conclude that Ms. Diaz’s story was
“transparently flimsy.” Brief in Opposition 16. Day in and day out,
the government secures convictions for the knowing importation of
drugs in just this way. Tr. of Oral Arg. 84. There was no need to
gild the lily by calling to the stand an “expert” in mindreading.
And there is certainly no cause for this Court to sanction the
practice.
To the contrary, there are sound reasons why
Rule 704(b) operates as it does. The problem of junk science in the
courtroom is real and well documented. See
Daubert v.
Merrell Dow Pharmaceuticals, Inc.,
509
U.S. 579, 589–590 (1993);
Kumho Tire Co. v.
Carmichael,
526 U.S.
137, 147 (1999); see also P. Huber, Galileo’s Revenge: Junk
Science in the Courtroom 15–17 (1991). And perhaps no “science” is
more junky than mental telepathy. After Hinckley’s trial, Congress
recognized as much when it adopted Rule 704(b) to remove from
federal courtrooms experts who claim to know what was inside a
man’s head at a particular moment in the past when he committed a
particular act.
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 Rule 704(b). See Part II,
supra;
ante, at 9. Eventually, the government felt it had to
backtrack after being confronted with too much evidence that some
couriers simply have no idea they are being used to carry drugs.
Flores, 510 Fed. Appx., at 595
. So now, the
government puts on witnesses to say
most couriers know. We
cannot be certain how many individuals sit in federal prison
because of the government’s past impermissible and mistaken
“expert” testimony that
all couriers know when they are
carrying drugs. About the only thing we can be sure of is that what
is good for the goose is good for the gander and that, thanks to
the Court’s opinion today, defendants will now recruit their own
warring experts. Ones who will seek to testify (not unlike Agent
Flood) that, in their experience, “most” drug couriers are kept in
the dark by cartels.
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 9. But
that role hardly matches Rule 704(b)’s promise that “matters” of
mens rea at trial belong to the jury “alone.”
V
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 Rule 704(b). But it
does not address what any other Rule of Evidence may have to say
about cases like this one. And, looking briefly to some of those
other Rules, I see reason for hope.
Take a few examples. Under Rule 402, any
evidence presented at trial must be “[r]elevant,” meaning it must
have a “tendency to make . . . more or less probable” a
“fact . . . of consequence in determining the action.”
Fed. Rules Evid. 401, 402. Yet, if the government is right that an
expert opinion about the mental state of “most” people like the
defendant is
not “about” the defendant’s mental state, it is
hard to see how that opinion might be relevant. After all, the
“fact of consequence” in cases like Ms. Diaz’s is whether the
defendant possessed the requisite
mens rea. And it’s hard to
see how the government can have it both ways—asserting in one
breath that opinions like Agent Flood’s are
not “about”
whether the defendant possessed the requisite mental state to
convict, while insisting in the next breath that those opinions
are relevant to (or, one might say, “about”) the defendant’s
mental state.
Rule 403 stands as another bulwark. That Rule
permits courts to “exclude relevant evidence” when its “probative
value is substantially outweighed by a danger of . . .
unfair prejudice.” Surely, in our system of justice—where we
recognize that each individual is presumed innocent and distinctly
endowed with free will and choice, where the individual is
responsible for his culpable mental states but not those of
others—testimony about what “most” people think bears minimal
probative value when the question at issue is what
this
individual thinks. Nor can the kind of testimony offered here hold
much probative value when juries, composed of the defendant’s
peers, are well suited to resolve questions of
mens rea
without “expert” assistance. Juries have managed that task for
centuries and, as we have long recognized, they are “fitted for it
by their natural intelligence and their practical knowledge of men
and the ways of men.”
Aetna Life Ins. Co. v.
Ward,
140 U.S.
76, 88 (1891).
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 Rule 403
challenges may be proper against such testimony. Brief for United
States 30–31.
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 may be highly tempted to do as it did in this case and
seek to throw in an “expert” on top of a seemingly strong
circumstantial case—just to be sure. But none of that means the
proffered testimony is likely to advance the promise of a fair
trial.
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 Fed. Rule Evid. 702(a) (1999)). I
struggle to see how a witness claiming to offer an opinion about
another person’s (or class of persons’) thoughts at a particular
moment in the past can meet any of those standards. No one, at
least outside the fortuneteller’s den, can yet claim the power to
conjure reliably another’s past thoughts. Testimony like Agent
Flood’s may be dubiously circular, too. For each time a law
enforcement agent takes the stand to say “most people know” and
that helps the government secure another conviction, he himself is
creating the very proof on which a government expert may purport to
rely in the next trial.
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.