For the Defense - Vol. 9, Issue 3 - 7

particular mental state, 'based on the defendant's membership
in a particular group.' " 19
Indeed, Ms. Diaz relied on this type
of evidence at her trial. She " called an automobile specialist
who testified that a driver of her particular car would almost
certainly not know that it contained drugs. " 20
According to Justice Jackson, Agent Flood's testimony did
not " deprive the jury of its ability to decide the last link in the
inferential chain: whether Diaz herself had the requisite mens
rea. " 21
Justice Gorsuch, joined by Justices Sotomayor and Kagan,
dissented. The dissent warned that the majority had given the
government a " powerful new tool. " 28
Moreover, they observed,
that tool is " unnecessary " in light of the government's " long
track record of success in proving mens rea the old-fashioned
way by presenting circumstantial evidence and appealing to
reasonable inferences. . . . There was no need to gild the lily by
calling to the stand an 'expert' in mindreading. " 29
Rather, " the type of mental-state evidence that Rule
704(b) permits can be of critical assistance to lay factfinders
tasked with determining a defendant's mental state as an
element of the alleged crime (or defense). " 22
Justice Jackson
offered two examples where such evidence could be helpful for
the defense. First, where a defendant suffers from a particular
mental health condition (like schizophrenia), an expert opinion
about the mental state of most people who suffer from that
condition " could help jurors better understand a defendant's
condition and thereby call into question a mens rea that
might otherwise be too easily assumed. " 23
for defendants who have suffered from domestic abuse.24
The same is true
An
expert's opinion about how victims of domestic abuse " respond
to aggression or react to violence . . . can play a pivotal role
in a defendant's attempts both to disprove the mens rea in a
number of serious crimes and to support a range of defenses,
including duress and self-defense. " 25
While noting the benefits, Justice Jackson also recognized
" that there are serious and well-known risks of overreliance
on expert testimony-risks that are especially acute in criminal
trials. " 26
But there are safeguards to those risks: " vigorous
cross-examination and careful refutation in closing argument; "
" other Rules of Evidence that might require exclusion; " and
the trial judge's role in " providing specific admonitions and
instructions when expert testimony about a relevant mental
state is introduced. " 27
The dissent focused its analysis on the word " about. " 30
Rule
704(b) " bars an expert from stating an opinion 'about whether
the defendant' had 'a mental state . . . that constitutes an
element of the crime charged.' " 31
" The word 'about' means
'[c]oncerning, regarding, with regard to, in reference to; in the
matter of.' " 32
According to the dissent, " 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. " 33
If any " doubt remain[s], " the dissent
says, " the Rule takes pains to emphasize, '[t]hose matters are
for the trier of fact alone.' " 34
The dissent outlined several potentially negative results from
the majority's ruling. First, " [a]llowing into [criminal] proceedings
speculative guesswork about a defendant's state of mind diminishes
the seriousness due them. " 35
Second, " [i]t risks the reliability of
the outcomes they produce. " 36 Third, " [i]t 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.' " 37
Fourth, " [i]t
diminishes our respect for the presumptively free person, his free
will and individuality, by encouraging the lazy assumption that he
thinks like 'most.' " 38
to play in criminal trials. " 38
Vol. 9, Issue 3 l For The Defense 7
Fifth, " it reduces the vital role juries are meant
" [T]hey can still decide whether the
For the Defense - Vol. 9, Issue 3

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