## Facts

- In a federal capital prosecution, the government sought to introduce DNA and serology evidence tied to firearms, a vehicle, and related items.
- Law enforcement recovered a .40 caliber Smith & Wesson handgun and magazine, among other evidence, and collected multiple swabs for DNA testing.
- The government’s DNA analyst, Carrie Zais Davis, performed STR DNA testing and issued reports with conclusions and statistical support.
- For a handgun swab (Item 1B22), Davis opined that McCluskey was the source of the major DNA profile in a mixture to a reasonable degree of scientific certainty.
- Certain results were classified by the laboratory as low copy number (LCN) DNA, including a magazine swab (Item 1B23B) with approximately 215 picograms of DNA and another item (Item 1132313) conceded to be LCN.
- McCluskey moved to exclude the government’s DNA/serology evidence and requested a Daubert hearing under Federal Rule of Evidence 702, challenging both standard DNA opinions and the reliability of the laboratory’s LCN testing.
- After extensive briefing and a targeted evidentiary hearing focused on LCN DNA, the court ruled on admissibility.

## Issues

1. Whether the government’s standard STR DNA testing and associated expert opinions were admissible under Federal Rule of Evidence 702 and Daubert.
2. Whether the NMDPS Laboratory’s LCN DNA testing results (including Items 1B23B and 1132313) were sufficiently reliable to be admitted under Rule 702 and Daubert.
3. Whether asserted weaknesses in interpretation, statistics, or stochastic effects required exclusion or instead went to weight for cross-examination.

## Decision

- The court granted the motion in part and denied it in part.
- The court denied exclusion of the government’s standard (non-LCN) STR DNA evidence and related expert opinions, finding Rule 702 and Daubert satisfied.
- The court excluded the NMDPS Laboratory’s LCN DNA results, including Item 1132313, because the government did not prove reliability by a preponderance of the evidence.
- The court treated most remaining criticisms of standard DNA interpretation and statistical presentation as matters for cross-examination rather than bases for exclusion.

## Legal Principles

- Under Federal Rule of Evidence 702 and Daubert, the proponent of expert testimony must show by a preponderance of the evidence that the testimony rests on reliable principles and methods reliably applied to the case facts.
- The trial judge must act as gatekeeper by assessing reliability and fit; general scientific acceptance does not automatically establish admissibility in a specific application.
- Standard STR DNA testing performed according to accepted protocols is generally admissible; many disputes about interpretation and statistics typically affect weight, not admissibility.
- LCN DNA testing requires careful scrutiny because low-template quantities heighten risks of stochastic effects (e.g., allelic drop-out, drop-in, peak imbalance) and increase interpretive subjectivity.
- Where a laboratory’s LCN protocol lacks adequate validation or is not shown to be consistently and rigorously applied, the resulting expert testimony may be excluded under Rule 702.

## Conclusion

The court admitted the government’s standard STR DNA evidence but excluded LCN DNA results from the NMDPS Laboratory after finding the government failed to establish the reliability of its LCN protocol and application by a preponderance of the evidence, as required by Rule 702 and Daubert.


United States v. McCluskey, 954 F. Supp. 2d 1224 (D.N.M. 2013)