## Facts

- Clifford Anderson, a janitor living and working in a Cook County apartment building, shot and killed the building manager and engineer on September 5, 1978.
- Anderson was indicted on two counts of murder and two counts of armed violence.
- Anderson’s defense at trial was insanity; he conceded sanity was the only material issue.
- The first trial ended in a mistrial after the jury could not reach a verdict.
- In a second trial held shortly thereafter, Anderson was convicted on all counts and sentenced to death after a bifurcated sentencing hearing.
- The defense called a psychiatrist, Dr. Jerome Katz, who interviewed Anderson and reviewed psychiatric/criminal records and related letters; Katz opined that Anderson could not conform his conduct to the law and probably could not appreciate the criminality of his acts at the time of the shootings.
- The defense also offered lay testimony from Anderson’s cousin/roommate and his sister concerning Anderson’s abnormal behavior and mental condition leading up to the shootings.
- The trial court allowed Dr. Katz to identify the reports he relied on, but barred him from disclosing their contents or otherwise explaining the reasons for his conclusions, ruling the underlying materials were inadmissible hearsay.

## Issues

1. Whether the trial court erred by preventing the defense psychiatrist from explaining the factual and diagnostic basis (including hearsay reports) for his insanity opinion while permitting only the ultimate conclusion.
2. Whether the restriction on the defense expert’s explanation was prejudicial where sanity was the sole contested issue and the State had to prove sanity beyond a reasonable doubt once the defense raised a reasonable doubt.
3. Whether the convictions and death sentence could stand given the evidentiary ruling affecting the guilt phase.

## Decision

- The Illinois Supreme Court reversed the convictions and remanded for a new trial.
- The court held the trial court erred by restricting the psychiatrist from explaining the bases for his opinion on sanity.
- The court found the error prejudicial because the jury was left with a bare expert conclusion without the foundation needed to evaluate its reliability, and sanity was the only material issue at trial.

## Legal Principles

- An expert may form an opinion using materials reasonably relied upon in the field even if those materials are not independently admissible.
- An expert may identify and describe the contents of such underlying materials to explain the basis of the opinion, not as substantive proof of the materials’ truth, but to permit the factfinder to assess the opinion’s weight and credibility.
- When insanity is the central issue, excluding meaningful explanation of the basis for psychiatric testimony can constitute reversible error if it may have affected the verdict.

## Conclusion

Because the trial court improperly prevented the defense psychiatrist from explaining the hearsay-based foundation for his insanity opinion, the jury lacked an adequate basis to evaluate the expert’s reasoning on the only contested issue, requiring reversal of the convictions and remand for a new trial.


People v. Anderson, 495 N.E.2d 485 (Ill. 1986)