US serial killer case opens door to using cutting-edge DNA data in courts

A judge in New York rejected a request on 23 September to disqualify the use of cutting-edge DNA sequencing as evidence in a case against an alleged serial killer. The ruling paves the way for a type of DNA analysis known as whole-genome sequencing — used to decipher ancient DNA in fossilized remains, for example — to be admitted as evidence in US criminal trials.

“This is a big step forward for the use of DNA evidence, because it will allow comparisons and matches with evidence that was previously considered too minuscule, too old or too badly degraded to be considered useful,” says Nathan Lents, a biologist at the John Jay College of Criminal Justice in New York City. “You can bet that cold-case units all over the country are going back through their evidence lockers to see if there are samples that can now be tested with a reasonable chance of success.”

A technology matures

The Gilgo Beach killings were a series of murders that occurred in Suffolk County, New York, between 1993 and 2011. Many of the victims were sex workers, and the bodies of some of them were found near the eponymous beach. New York architect Rex Heuermann was charged with seven of the murders in 2023 and 2024 partially on the basis of hairs found on the victims.

In 2010, investigators concluded that there wasn’t enough genetic material in the hairs for conventional forensic technology to identify whose they were. But since then, genomic technology has matured at a fast pace.

Forensic scientists still identify suspects from hair and other samples using the conventional polymerase chain reaction (PCR) method, which can amplify snippets of DNA called short tandem repeats (STRs). Today, however, scientists can also sequence whole genomes and look at single-letter variations in the DNA to zero in on a person of interest. This technology has the added benefit of being able to analyse severely degraded samples — from Neanderthal remains to hairs in the Gilgo Beach case. But it has typically been used only during investigations, and the results have not been widely presented as evidence before juries.

The controversial company using DNA to sketch the faces of criminals

The prosecution in the Gilgo Beach case contracted the company Astrea Forensics in Santa Cruz, California, to analyse the hairs found on the victims. Because they were rootless, they hadn’t yielded enough DNA for conventional STR profiling. (Rootless hairs are mostly made of keratin and don’t contain much genetic material, Lents says.)

But Astrea was able to sequence the small amount of genetic material in the hairs and then use statistical-analysis software to scan the DNA for single-nucleotide polymorphisms (SNPs) — single-letter differences in people’s genetic codes. Even in a degraded sample, whole-genome sequencing followed by this statistical analysis can spot thousands of SNPs: enough to pinpoint an individual’s unique pattern, Lents says.

Next, scientists at Astrea compared the SNP profiles they obtained with profiles stored in genealogy databases and looked for matches. People submit their DNA to genealogy services, such as 23andMe and Ancestry, and these companies return SNP profiles that people can then upload to websites such as GEDMatch to locate potential relatives. Users have the option to make the data available to forensic genealogists — and these data are what Astrea used to zero in on Heuermann and his family.

Setting precedent

The defence team in the Gilgo Beach case initially challenged the validity of Astrea’s DNA-analysis methods — which were developed by palaeogenomics researcher Richard ‘Ed’ Green at the University of California, Santa Cruz. (Green declined to comment for this article, given the ongoing prosecution.) The defence argued that the statistical methods used by Astrea were unique, and questioned whether they had been sufficiently validated.