## Facts

- James Bowman was prosecuted for murder in California.
- Defense counsel retained neurologist Arthur Kowell to evaluate Bowman and ordered a positron-emission tomography (PET) scan.
- The PET scan reportedly showed decreased temporal-lobe functioning (temporal-lobe hypometabolism).
- The defense sought to introduce expert testimony that temporal-lobe hypometabolism can be consistent with decreased impulse control, supporting a mental-state/impulse-control defense.
- The expert conceded limits to the proposed inference, including inability to diagnose a specific disorder from the scan alone, lack of scientific literature establishing general acceptance of PET as a diagnostic-inference tool for this purpose, and inability to tie scan findings to Bowman’s mental state at the time of the offense.
- The expert also acknowledged that other factors (e.g., depression or medications) could affect PET-measured temporal-lobe metabolism.

## Issues

1. Whether, under California’s Kelly/Frye general-acceptance standard for novel scientific evidence, the trial court properly excluded PET-scan-based expert testimony offered to show diminished impulse control relevant to the time of the offense.
2. Whether excluding the PET evidence constituted an abuse of discretion warranting reversal of Bowman’s murder conviction.

## Decision

- The Court of Appeal affirmed Bowman’s murder conviction.
- The court upheld the trial court’s exclusion of the PET-scan evidence under Kelly/Frye.
- The court concluded the trial judge acted within discretion in finding the proffered forensic use of PET imaging too scientifically uncertain and insufficiently accepted in the relevant scientific community.

## Legal Principles

- Under California’s Kelly/Frye framework, expert testimony based on a scientific technique (or a disputed application of a technique) is inadmissible unless the proponent shows the technique and its specific application are generally accepted as reliable in the relevant scientific community.
- General clinical use of a technology does not establish admissibility for a different, forensic purpose; the admissibility inquiry focuses on the reliability and acceptance of the particular inference the testimony asks the jury to draw.
- Courts may exclude scientific evidence where the expert’s own concessions show the proposed causal link is not well-validated, is not reliably attributable to the individual defendant, or cannot be connected to the defendant’s mental state at the legally relevant time.
- Appellate review of such scientific-evidence rulings is for abuse of discretion; exclusion is upheld if it falls within the range of reasonable evidentiary choices.

## Conclusion

The court held that PET-scan testimony offered to infer a defendant’s impaired impulse control at the time of a homicide did not satisfy California’s Kelly/Frye general-acceptance requirement where the expert could not reliably connect the scan to diagnosis, causation, or the time of the offense, and it therefore affirmed the conviction.


People v. Bowman, No. G048874, 2014 WL 718416 (Cal. Ct. App. Feb. 25, 2014)