Jury and Expert Roles

Jury and Expert Roles

Once the causal question has been defined, someone must answer it, and the product test divides that work between two sets of participants. Psychiatric witnesses understand the illness, while jurors speak for the community on whether the accused deserves blame. The original opinion drew the line between them in one place, and the District of Columbia court later moved it after watching the test operate. The two parts below follow that sequence, beginning with the division Durham announced.

The Original Division of Labor

Durham gave psychiatrists a defined job: their principal function in court is to inform the jury of the character of the accused's mental disease or defect.¹ The jury then decides the ultimate questions of fact, which the suggested instruction framed as whether the accused suffered from a diseased or defective mental condition at the time of the act and whether the act was the product of that abnormality.² The second question is the but-for inquiry developed earlier, namely whether the accused would not have committed the act but for the disease.³ The assignment fits what psychiatrists are equipped to do. The Supreme Court described the same kind of expert work in Ake v. Oklahoma: psychiatrists gather facts through examination and interviews, analyze what they find, and draw conclusions about the accused's mental condition and about how a disorder may affect behavior. They can also recognize symptoms that a layperson would miss or misread and explain to jurors why those observations matter.⁴

The opinion left the final question with the jury for a reason rooted in what that question asks. Whether an act deserves blame is a moral judgment, and Durham reasoned that leaving the ultimate question to the jury lets it apply inherited ideas of moral responsibility, under the precept that the community's collective conscience does not permit punishment where it cannot impose blame.⁵ A psychiatrist's training equips the witness to describe an illness; it gives no special authority to decide when blame should lapse, so handing the final question to the expert would transfer a community judgment to a profession. A practical reason points the same way. Psychiatrists disagree widely and frequently about what counts as mental illness and what diagnosis fits given behavior, which is why juries remain the primary fact finders and must resolve the disagreements among the experts on the evidence each side offers.⁶

The same division explains why the jury is not confined to a list of symptoms. Under the right-wrong test the inquiry had rested on one symptom, whereas Durham sent testimony about symptoms and manifestations, together with other relevant evidence, to the jury on the ultimate questions of fact.⁷ The jury's inquiry may still include whether the accused knew right from wrong, acted under an irresistible impulse, or had lost the power of the will, but each of those is evidence bearing on the ultimate question and not a condition the defense must satisfy.⁸ The reason is that medical science recognizes that particular symptoms do not necessarily accompany even serious mental disorders, so a rule demanding a given symptom would exclude illness that is genuine. The question becomes whether the accused acted because of a mental disorder, and a missing symptom does not answer it.⁹

Students lose this point when they treat the psychiatrist's diagnosis as the verdict, since the expert supplies the character of the disease and the jury decides whether the act was its product.¹⁰ Experience soon showed that this line was hard to hold, and the next part explains how the court adjusted it.

The Later Limit on Experts

Experience under the product test led the District of Columbia court to narrow the expert's part. In Washington v. United States, decided in 1967, the court held that psychiatrists could no longer testify whether the offense was the product of mental illness.¹² Their testimony was confined to a description of the defendant's mental condition, and the jury decided whether that condition was a mental disease or defect and whether the crime was a product of it.¹³ The limit refined the role of experts without removing them. Psychiatrists were still to explain how the defendant's disease or defect relates to the alleged offense, meaning how the development and functioning of the defendant's behavioral processes may have influenced the conduct, but they were to withhold the conclusion on the ultimate issue.¹⁴

The reason lies in how much weight the word product carried. Once a mental disease in the legal sense was established, the outcome turned on productivity, so an expert who testified in those terms raised the concern that the ultimate issue had been handed to the experts instead of being kept for jurors who represent the community.¹⁵ A jury that hears a qualified witness state the conclusion has an easy path to adopting it, and the weighing the jury was supposed to perform shrinks into acceptance of a label. The court that later abandoned Durham described the result as trial by label and observed that conclusory testimony invited the jury to abdicate its responsibility as ultimate decision maker.¹⁶ The proof itself added a second problem, because a witness could sometimes affirm that an act was a product of illness but could rarely say that it was not, so an expert conclusion on product tended to favor the defendant. Barring that conclusion removed the imbalance, a difficulty the next section develops with the other criticisms of the test.¹⁷

Modern federal evidence law reflects a similar concern in a different setting. Rule 704(b) bars an expert in a criminal trial from stating an opinion that the defendant had or lacked a mental state or condition that is an element of the crime or of a defense, and its purpose is to confine psychiatrists to presenting and explaining diagnoses and to keep them from speaking in legal or moral constructs.¹⁸ That rule is not a product-test rule, and it speaks to the mental states at issue under modern definitions of insanity. The logic is nonetheless the same: the expert explains the illness, and the factfinder draws the legal conclusion.

The two questions differ in a single respect, which is whether the witness announces the answer to the causal question or supplies the material from which the jury reaches it. Students lose this issue when they assume that an expert opinion that the act was a product of the illness remains proper because experts may discuss causation in general, since after the limit the expert may describe how the disease relates to the offense but may not state the product conclusion.¹⁹