United States v. Shea

The federal government (plaintiff) charged Anthony Shea (defendant) with bank robbery and related offenses. The government alleged that one of two masked bank robbers left bloodstains at the bank and on a van that was used as a getaway vehicle. The government sought to introduce expert testimony from a Federal Bureau of Investigation (FBI) forensic scientist who had compared the DNA extracted from the bloodstains with Shea’s DNA and determined that the DNA samples matched. The expert planned to testify that the probability of finding a similar match between the bloodstains and any DNA sample drawn randomly from the total population of White people was one in 200,000. Before trial, Shea moved to exclude the expert’s testimony about the random-DNA-match probability, arguing that the risk was too great that the probability evidence would mislead the jury. Shea argued that an estimate of random-DNA-match probability would have been meaningless if the DNA-profile match were in fact false; therefore, jurors would understand the significance of the information only if a false-match error rate were combined with the random-match probability. Because the FBI laboratory did not calculate its false-match error rate for the type of test used, Shea proposed using the overall DNA-testing industry’s false-match error rate for that test. However, the parties did not agree on the industry’s false-match error rate. The federal district court denied Shea’s motion and admitted the expert testimony. The jury convicted Shea. The federal district court then issued an opinion to explain why it admitted the probability evidence.