The decision by Judge Tim Mazzei is a slam dunk for Suffolk County DA Ray Tierney, whose case against Heuermann hinges largely on DNA.

“If I wasn’t confident in this case I would’ve never brought it to trial,” Tierney told reporters.

Heuermann’s lawyer, Michael Brown, had challenged the DNA evidence and sought to have his client tried separately for each of the seven sex workers he is accused of killing.

Mazzei ruled earlier this month that crucial DNA evidence could be used in the case against the 61-year-old accused serial killer – which Brown challenged, leading to Tuesday’s ruling.

The DNA matches link Heuermann to seven sex workers found dead along a desolate stretch of Long Island – Valerie Mack, 24, Melissa Taylor, 20, Megan Waterman, 22, Melissa Barthelemy, 24, Maureen Brainard-Barnes, 25, Sandra Costilla, 28, and Amber Lynn Costello, 27.

The bodies were dumped between 1993 and 2010, but the murders remain unsolved until former NYPD bigwig Rodney Harrison took over as Suffolk County police commissioner and reopened the case – leading to Heuermann’s arrest in July 2023.

Investigators then carried out two thorough searches of the Heuermann home in Massapequa Park, which led to the alleged discovery of a grisly “planning document” allegedly kept by the accused killer, including a “lessons learned” section.

“I think a big consideration by the court, which was stated in their decision, was that planning document,” Tierney said. “That planning document talks about murders that had occurred, that are about to occur and that are going to occur in the future.”

The hulking architect, who has denied he was behind the grisly slayings, has since been held without bail while the case crawls toward a trial.

Brown has called the DNA evidence “magic,” and moved to have it thrown out while asking that each of the murders be the subject of separate trials.

“We’re not making motions for the sake of making motions,” he said outside the courtroom. “We’re making motions because we are confident in the law and confident in our position.

“Ultimately, we do not make the decision,” he said.

The DNA evidence, processed by Astrea Labs, was tested using high-tech science that allowed damaged samples to be used for the first time in a New York State courtroom.

“Ultimately, we do not make the decision,” he said.

Brown argued on Sept. 3 that the lab is not licensed in the state and that using the evidence would violate Empire State health laws.

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Meanwhile Tierney said he plans to call “well over” 100 witnesses from 15 different states to testify at the upcoming trial, with more than 6.5 million documents entered into evidence.

Brown called the 100 terabytes of evidence “a mountain of a mountain.