United States ex rel. DiGiacomo v. Franzen

In 1977, a jury convicted James DiGiacomo (defendant) of rape, deviate sexual assault, aggravated kidnapping, and battery. A woman testified that DiGiacomo forced her at knifepoint to drive to a cornfield and then raped her in the cornfield. The prosecution (plaintiff) called an expert witness, Sally Dillon, to testify that hairs found in the woman’s car were microscopically similar to a sample of DiGiacomo’s hair. Over DiGiacomo’s objection, Dillon stated that based on a recent study, the statistical probability that the hair in the woman’s car belonged to someone other than DiGiacomo was one in 4,500. DiGiacomo did not cross-examine Dillon about her hair-comparison testimony. After several hours of deliberations, the jury asked the court whether Dillon’s hair comparison had positively proven that DiGiacomo had been in the woman’s car. The trial judge responded that he could not answer that question because it was the jury’s duty to determine the facts based on the evidence presented at trial. After exhausting his appeals in Illinois state court, DiGiacomo filed a habeas corpus petition in federal district court. DiGiacomo argued that Dillon’s statistical-probability statement had violated his constitutional due-process rights; instead, Dillon’s testimony should have been limited to stating that the two hair samples were similar. The federal district court denied DiGiacomo’s petition, and DiGiacomo appealed to the United States Court of Appeals for the Seventh Circuit.