A new DNA testing method could play a big role in the case against the accused Gilgo Beach killer

At the heart of the case against the man accused of the Gilgo Beach killings is DNA evidence — but the novel way that evidence was tested may now determine whether prosecutors can use it against their prime suspect, Long Island architect and family man Rex Heuermann.

A Suffolk County judge is set to decide Wednesday whether the results of that testing method, which has never been used in a New York courtroom, should be permitted in Heuermann’s trial, which could start next year.

Heuermann is charged with murder in the deaths of at least seven women spanning three decades. He has pleaded not guilty.

In arguments before the judge earlier this year, prosectors argued the technology they used in the Gilgo case – known as whole genome sequencing – bolsters testing that’s already widely accepted and helps to extract evidence that would otherwise be impossible to get, such as from rootless hairs or degraded samples. Investigators used the technology to determine hairs found on several of the victims belonged to Heuermann or someone in his immediate family, court records show.

Heuermann’s defense team, meanwhile, argues the technology is largely unproven.

“It’s a critical ruling as much as anything that has to do with something as powerful as DNA evidence. It’s going to move the needle,” said CNN legal analyst Joey Jackson. “It would be a huge win for the prosecutors if it were admitted and a huge blow to the defense.”

Jackson said the evidence could be devastating for Heuermann because prosecutors would be able to make the case for jurors that he was with the victims in their final moments. Without it, the defense would have an easier time arguing its case knowing a key piece of evidence wouldn’t be considered by a jury.

If Judge Timothy Mazzei rules against prosecutors, however, they still have more to work with.

“At the end of the day, they have so many bites of the apple with this guy,” Jackson said. “There’s so much other evidence. The judge can sleep at night and say, ‘I didn’t kill their case. I just took one tool out of their toolbox that has 20 different tools in it.’”

Heuermann was arrested in July 2023 and charged with murder in the killings of three women whose bodies were discovered bound with belts or tape and wrapped in burlap along a stretch of Ocean Parkway in Gilgo Beach in 2010.

Those victims, Melissa Barthelemy, Megan Waterman and Amber Costello – along with a fourth woman, Maureen Brainard-Barnes, whose death Heuermann was charged in while in custody – became known as the “Gilgo Four.”

Two second-degree murder charges were added in June 2024 for the deaths of Jessica Taylor and Sandra Costilla. Taylor was killed in 2003, and Costilla in 1993.

In December, Heuermann was charged with murder in the death of a seventh woman, Valerie Mack, in a superseding indictment.

Heuermann’s July 2023 arrest was a major event in the area. Since the discovery of the bodies began in 2010, the mystique of the Long Island Serial Killer grew with each year the murders went unsolved. It quickly became the biggest mystery on Long Island, prompting books, articles and documentaries all while fear grew among residents knowing the killer was still out there.

Heuermann now spends his days at the Suffolk County correctional facility.

Expected arguments

The defense contends the DNA analysis used by prosecutors lacks broad acceptance within the scientific community and should not be allowed as evidence in the trial.

The analysis was conducted by Astrea Forensics, a company that specializes in whole genome sequencing — a type of DNA analysis that can be used for difficult-to-treat samples.

Whole genome sequencing is “a method that attempts to read nearly all of a person’s DNA, covering the entire genetic code of about 3 billion bases,” or letters, said Daniele Podini, an associate professor at George Washington University.

“I think that it was used in this case because the DNA in hair is very degraded/fragmented and the conventional Short Tandem Repeat (STR) analysis is not as likely to be successful,” Podini told CNN via email. “STR analysis looks only at specific regions in the genome where short DNA sequences repeat multiple times.”

The key difference, Podini said, is conventional testing provides a limited DNA “fingerprint,” like a barcode on a supermarket product, while whole genome sequencing (WGS) offers a full genetic “blueprint” with much more detailed insights.

Though the type of analysis has “not yet been subject to an admissibility hearing in the State of New York,” prosecutors said in their argument to the judge earlier this year, the technique is commonly used across numerous scientific and forensic fields, including virology, health care and criminal justice — and by law enforcement, prosecutors and defense attorneys.

“WGS is an advancement in DNA testing which enables more comprehensive collection and evaluation of DNA and has wide application throughout the relevant scientific communities,” prosecutors said. “It has been accepted by the CDC, the FDA, paleontologists, virologists, and the medical communities.”

New technologies are always up for examination before becoming routine, said Nathan Lents, a professor of biology at the City University of New York’s John Jay College of Criminal Justice.

“Forensic methods are subject to intense legal scrutiny before they are accepted as common practice, and that’s what we are seeing here,” Lents said. “This is the normal way that new techniques are introduced into the legal forensic toolkit, in test cases with a great deal of scrutiny and expert testimony.”

With or without DNA, prosecutors plan to build their case from multiple angles

If the DNA testing method in the case is thrown out, Suffolk County prosecutors could rely on other evidence like the content allegedly discovered on Heuermann’s devices, including a planning document outlining a strategy for future killings, or the newspapers and magazines allegedly found during a search warrant of his home that talked about the killings of the women.

According to a bail application, the manual contained headings such as “Supplies” and “Problems,” with “DNA” listed as the top item under the latter. A section titled “body prep” detailed steps to clean, dismember and move bodies, while another called “post event” appeared to list tasks to avoid apprehension, including having a story set.

Prosecutors also have cell phone data and pings from cell towers that point to Heuermann, the eyewitness descriptions of him and his truck, the Chevrolet Avalanche, according to an official with knowledge of their strategy. They also have mitochondrial DNA that still points to Heuermann but would be more work for prosecutors to establish that it was Heuermann – and not someone related to him – that carried out the murders, the official said.

Though a trial date hasn’t been set for Heuermann, it’s expected to be sometime next year and will see prosecutors call witnesses who can testify to the legitimacy of the DNA, law enforcement that recovered the bodies and medical examiners who inspected the bodies, the official said.

Meanwhile, Michael Brown, the defense attorney for Heuermann, said Wednesday’s decision is important for their case but not essential.

“If we don’t prevail on this, it’s OK – we still have the ability to attack this before a jury,” Brown told CNN. “I’m confident that a jury would disregard this new methodology.”

Part of the defense’s strategy will include not only fighting the DNA evidence but also highlighting discrepancies in the case, such as an allegation that law enforcement had another suspect they were going to arrest before Heuermann was taken into custody, according to a source with knowledge of the defense’s thinking.

They also plan on digging up corruption in the history of Suffolk County law enforcement, something critics have long pointed to as being a main reason the Gilgo serial killer was not caught earlier, according to the source.

How common is the technique?

Though it’s never been used in a case in New York state, experts say, the use of whole genome sequencing as a DNA analysis method has been used for some time.

“The technique is legitimate and reliable and has been used in the research and clinical setting for many years now,” Lents, the biology professor, told CNN.

“It is only coming into the forensic realm because forensics always trails a few years behind the scientific advances, because the courts want to see any new technique be deployed, analyzed and scrutinized for years before it is applied in a criminal case where someone’s life or liberty is at stake,” he added.

The US Food and Drug Administration uses whole genome sequencing to identify pathogens during foodborne illness outbreaks, the agency says on its website. Public health researchers use it to understand why certain bacteria cause more severe illness or show greater resistance to antibiotics, according to the Centers for Disease Control and Prevention.

Despite this, Heuermann’s attorney argued this type of DNA evidence hasn’t gotten the general acceptance of the scientific community.

“The prosecution has failed to meet this burden,” defense attorneys wrote. “At best, the evidence presented demonstrates that the academic debate surrounding this paradigm shifting methodology is in its infancy, far short of the general acceptance required by law. Accordingly, this court must preclude the admission of such evidence.”

Prosecutors, however, say the latest advancements in forensic testing are not only reliable, but widely accepted.

“These facts demonstrate that the methodology has moved well beyond the novel or experimental stage,” wrote Suffolk County prosecutors. “This is not ‘magic’ – it’s science.”

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