Forensic DNA, PCR, and a Contested Sample

Edward Blake was a private forensic consultant whose career included high-profile criminal cases. He performed DNA testing in the Roger Keith Coleman matter and retained a minute frozen sample in his California laboratory rather than returning it to Virginia. The custody of that sample was contested for years, and litigation and public requests sought independent retesting while the biological material remained in cold storage.

The polymerase chain reaction, which permits exponential amplification of targeted DNA segments, transformed forensic practice by enabling reliable profiles from trace or degraded stains that older methods could not process. PCR-based STR assays and later refinements such as miniSTRs and direct PCR have allowed laboratories to obtain profiles from tiny deposits, sometimes as small as a pinhead, and to do so in days rather than weeks.

Because PCR made post-conviction testing technically feasible, it has been central to many efforts to revisit old cases. Advocacy groups and registries report that 614 people in the United States have been exonerated after DNA testing, a result that has driven renewed attention to evidence preservation and to legal rules that govern access to biological material.

If evidence is preserved and available for independent analysis, then old uncertainties can often be resolved; if it is lost or consumed, crucial questions may never be answered. Consequently, courts, laboratories, and advocates continue to weigh scientific capacity, chain-of-custody safeguards, and the public interest when deciding who may test legacy evidence. Many laboratories have developed protocols for low-copy-number samples, and courts have sometimes required independent verification when the stakes are high.