## Facts

- Two masked, gloved men armed with revolvers broke into a New Hampshire bank about an hour after closing on August 4, 1995.
- Investigators found bloodstains inside the bank and in a stolen minivan believed to be the getaway vehicle; one robber appeared to have cut himself entering through broken glass.
- The government charged Anthony Mark Shea with attempted bank robbery and related offenses.
- The prosecution sought to introduce FBI expert testimony using PCR-based DNA testing comparing blood from the scene and minivan to Shea’s blood.
- The FBI expert concluded Shea’s DNA profile matched the source of several bloodstains and reported a random match probability of 1 in 200,000 within the Caucasian population.
- Shea moved pretrial to exclude both the DNA “match” opinion and the random match probability statistic.

## Issues

1. Whether the FBI’s PCR-based DNA testing procedures and resulting statistical calculation were sufficiently reliable to be admitted as expert testimony under Federal Rule of Evidence 702 and the Daubert reliability framework.
2. Whether the random match probability testimony should be excluded under Federal Rule of Evidence 403 because jurors might be misled or give the statistic undue weight.

## Decision

- The court denied Shea’s motion to exclude the DNA evidence.
- The court held the FBI’s PCR testing and associated statistical methods were reliable enough for admission under Rule 702.
- The court held the absence of a quantified, lab-specific false-positive error rate did not require exclusion; it affected weight rather than admissibility.
- The court held the probative value of the DNA match and random match probability was not substantially outweighed by risks identified in Rule 403, given the availability of cross-examination, competing experts, and limiting jury instructions.
- Shea was later convicted; the court of appeals affirmed the admission of the PCR DNA evidence.

## Legal Principles

- Under Rule 702 and Daubert, the court must assess both the validity of the scientific technique and the reliability of its application, including laboratory procedures and statistical methodology.
- A precise quantified error rate is a relevant reliability consideration, but the lack of a lab-specific false-positive rate does not automatically bar admission when other indicia of reliability (validation, quality controls, scientific support, acceptance) are shown.
- Random match probability evidence may be admissible when grounded in accepted population genetics methods; disputes about assumptions and potential error generally go to weight.
- Under Rule 403, statistical DNA evidence is not excluded solely because jurors might misinterpret it; courts may manage that risk through cross-examination, competing testimony, and careful instructions.

## Conclusion

The court admitted FBI PCR-based DNA match testimony and a 1-in-200,000 random match probability statistic, finding the methods reliable under Rule 702 and the risk of juror confusion manageable under Rule 403 despite the absence of a lab-specific false-positive error rate.


United States v. Shea, 957 F. Supp. 331 (D.N.H. 1997)