## Facts

- James G. DiGiacomo, an Illinois prisoner, was convicted of rape, deviate sexual assault, aggravated kidnapping, and battery arising from an attack on Patricia Marik.
- Marik testified that she was abducted at knifepoint from a Naperville tavern, forced to drive to a cornfield, and assaulted; she identified DiGiacomo as the assailant.
- Investigators recovered hair samples from Marik’s automobile after the incident.
- A state forensic criminologist compared the recovered hairs to DiGiacomo’s hair sample and concluded they were microscopically similar.
- Over objection, the expert testified to a numerical probability—based on a study—that the chance the hair belonged to someone other than DiGiacomo was 1 in 4,500.
- During deliberations, the jury asked whether hair sampling “positively” proved DiGiacomo had been in the automobile.
- The trial judge answered that there was no “positive identification,” only expert opinion testimony stated as a probability, and instructed the jury to determine the weight of that testimony.
- After state proceedings, DiGiacomo sought federal habeas relief under 28 U.S.C. § 2254, claiming the probability testimony denied due process; the district court denied relief.

## Issues

1. Whether admitting expert hair-comparison testimony stated as a numerical probability (1 in 4,500), in context of the whole trial and the jury’s question, rendered the trial fundamentally unfair in violation of due process, warranting federal habeas relief.

## Decision

- The Seventh Circuit affirmed the district court’s denial of the habeas petition.
- The court held that the admission of the probability testimony did not violate any constitutional right.
- The court concluded the challenged evidence, considered with the trial court’s response to the jury and the other proof of guilt, did not so infect the trial with unfairness as to amount to a due process violation.

## Legal Principles

- Federal habeas relief does not lie for mere state-law evidentiary error; the question is whether the error rendered the trial fundamentally unfair and thus violated due process.
- The due process standard for evidentiary claims on habeas is whether the challenged ruling “so infected the trial with unfairness” that the conviction is a denial of due process.
- Admission of numerical probability testimony tied to forensic comparison evidence is not per se unconstitutional; the constitutional inquiry is contextual and record-based.
- A trial court’s clarification that expert probability testimony is not “positive identification,” coupled with an instruction leaving weight and credibility to the jury, mitigates the risk that jurors treat the statistic as conclusive proof.
- Where there is substantial independent evidence of identity (including eyewitness identification), probability testimony used as corroboration is less likely to create fundamental unfairness.

## Conclusion

The Seventh Circuit held that, on federal habeas review, the hair-comparison probability testimony—tempered by the trial judge’s instruction and supported by other evidence including the victim’s identification—did not render the state trial fundamentally unfair, so due process was not violated and habeas relief was properly denied.


United States ex rel. DiGiacomo v. Franzen, 680 F.2d 515 (7th Cir. 1982)