Accused Gilgo Beach serial killer Rex Heuermann appeared in a Long Island courtroom Tuesday with a chilling gaze — as prosecutors dumped a “massive amount” of evidence in his lap.

Suffolk County prosecutors said the brief court appearance is just the beginning of what promises to be a lengthy criminal case, with Heuermann’s lawyers handed eight terabytes of evidence to review.

“This is a 13-year case, so as you see, we have a great deal of information, evidence, photographs, reports to provide to the defense counsel,” Suffolk DA Raymond Tierney told reporters outside the courthouse.

“We’ve begun that process. And that’s just the beginning,” he said. “We’re gonna continue to do that on a rolling basis.”

Heuermann, 59, is charged with murder in the deaths of three women whose bodies were found dumped along Gilgo Beach in December 2010 — Melissa Barthelemy, Megan Waterman and Amber Lynn Costello.

He is also the prime suspect in the death of a fourth woman, Maureen Brainard-Barnes.

Heuermann, an architect from Massapequa Park, was arrested on July 13 outside his Midtown Manhattan offices and is being held at the Suffolk County Jail without bail.

Facing a judge for the second time in the case Tuesday, the hulking suspect, his hair matted down, at one point scanned the audience with an icy stare, as if looking for someone.

He didn’t speak during the proceeding, to which he wore a blue shirt and black suit jacket, paired with khaki pants with grenade pockets on the sides — and his hands handcuffed in the front.

Some of the victims’ relatives were in court, though Heuermann’s wife, Asa Ellerup — who has said she was shocked by his arrest and has since filed for divorce — was not among those in the audience.

Suffolk County and state police descended on the accused killer’s house following his arrest, combing through the property including by bringing in an excavator to dig up the backyard in a search for body parts or “trophies.”

Authorities said they found a walk-in vault in the basement and removed nearly 300 weapons from the home, but have not said if any significant evidence was recovered.

Ellerup and her two children, Christopher Sheridan, 33, and Victoria Heuermann, 26, returned to their home last week after police concluded their search — only to find it in shambles, she told The Post Monday.

Who were the Gilgo Beach victims?

Suspected serial killer Rex Heuermann — a New York City architect and married dad of two — was arrested in connection with the long-unsolved Gilgo Beach murders. The arrest is tied to the so-called “Gilgo Four,” women found wrapped in burlap within days of each other in late 2010.

The years-long investigation that led to the arrest revolved around the discovery of more than 10 sets of human remains along Ocean Parkway near Gilgo Beach in Suffolk County between December 2010 and April 2011.

Most victims were petite female sex workers with green or hazel eyes. But there were also two exceptions: a 2-year-old girl and a young Asian man.

Melissa Barthelemy, 24

• Barthelemy was a sex worker who lived in the Unionport section of the Bronx and dreamed of one day opening her own beauty salon. She was last seen alive in her basement apartment on Underhill Avenue on July 12, 2009. Heuermann was charged for Barthelemy’s murder in July 2023.

Maureen Brainard-Barnes, 25

• Brainard-Barnes was living in Norwich, Connecticut. She went missing after taking an Amtrak train from New London, Connecticut, to Grand Central Terminal in Manhattan on July 6, 2007. Her remains were found in December 2010. Heuermann was charged for Brainard-Barnes’ murder in January 2024.

Amber Lynn Costello, 27

• Costello, 27, was a sex worker and heroin addict who lived in West Babylon, New York, at a home with a woman and two men. She advertised on Craigslist and Backpage to support her and her roommates’ drug habits. Costello was found on December 13, 2010, after having been last seen leaving her home September 2, 2010. Heuermann was charged for Costello’s murder in July 2023.

Megan Waterman, 22

• Waterman, a 22-year-old mom of one, was last seen on June 6, 2010. She lived in Scarborough, Maine, and earned a living as an escort. She was last seen by her family boarding a New York-bound Concord Trailways bus in Maine. Her body was found on December 13, 2010, on the north side of Ocean Parkway, near Gilgo Beach. Heuermann was charged for Waterman’s murder in July 2023.

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Jessica Taylor, 20

• Remains belonging to Jessica Taylor, a 20-year-old woman working as an escort in New York City, were found in a wooded area in Manorville on July 26, 2003. Her additional remains — initially labeled “Jane Doe No. 5” — were discovered on March 29, 2011, along Ocean Parkway.

Valerie Mack, 24

• Valerie Mack was 24 years old and living in Philadelphia when she went missing. She worked as an escort, using the alias “Melissa Taylor.” Relatives last saw Mack in the spring or summer of 2000 in Port Republic, New Jersey, but she was never reported as missing to the police. Her partial skeletal remains were found in Manorville in September 2000 but were initially known as “Jane Doe No. 6.” More bones were found on April 4, 2011, along Ocean Parkway.

Unidentified Asian man

• The skeletal remains of a yet-to-be-identified Asian man were found along Ocean Parkway on April 4, 2011. It is estimated that the man was between 17 and 23 years old at the time of his death. He was approximately 5 feet 6 inches tall with bad teeth.

‘Peaches’ and her daughter

• An African American woman’s partial remains were discovered in Hempstead Lake State Park back in 1997, and she had become known as “Peaches” because of a bitten tattoo of a peach on her left breast. On April 4, 2011, police uncovered the remains of a toddler, who was about 2 years old at the time of her death. DNA testing confirmed that one of the skeletons was that of the 2-year-old girl’s mother, “Peaches.”

Karen Vergata

• A victim previously referred to as Jane Doe No. 7 has been identified as 34-year-old Manhattan woman Karen Vergata. Vergata is believed to have disappeared around Feb. 14, 1996; two months later, her legs were found in a plastic bag at a park near Fire Island’s Blue Point Beach. At the time of her disappearance, Vergata was believed to have been working as an escort. Two sets of Vergata’s remains were identified in August 2023.

Shannan Gilbert, 23

• Gilbert was a Craigslist escort who lived in Jersey City, traveled with her driver Michael Pak from Manhattan to meet a client, Joseph Brewer, at his home in the Oak Beach Association on the morning of May 1, 2010. She spoke with two neighbors before disappearing. Her body was discovered in a marsh near Oak Beach — about half a mile from where she was last seen alive — on December 13, 2011.

Jessica Taylor, 20

• Taylor, a 20-year-old woman working as an escort in New York City, were found in a wooded area in Manorville on July 26, 2003. Her additional remains — initially labeled “Jane Doe No. 5” — were discovered on March 29, 2011, along Ocean Parkway.

Sandra Costilla

• Costilla was murdered in 1993 but had not been included among the so-called Gilgo Beach victims — until now. Investigators suspected convicted serial killer John Bittrolff in Costilla’s death, but he was never charged in her slaying — which remains one of several unsolved Long Island murders.

She said the case has left the family traumatized.

“My children cry themselves to sleep,” she said. “I mean, they’re not children. They’re grown adults but they’re my children, and my son has developmental disabilities and he cried himself to sleep.”

Ellerup said cops left the house so disheveled that they could barely find a chair to sit in, had no beds to sleep in and found that the bathtub had been cut up.

Tierney said he will prosecute the case himself.

Outside the courthouse, defense attorney Michael Brown urged the public not to prematurely judge his client.

“The press has convicted my client without seeing a shred of evidence,” Brown said. “So, he doesn’t stand a chance with the press. And we’re not going to try the case in the press.

“I doubt that any one of you for a moment have even contemplated the possibility that they have the wrong guy,” he said. “What we’re going to do is defend this case in a courtroom. … Where we have 12 fair and impartial jurors, where we have a fair and impartial judge.

“Where words like ‘presumption of innocence’ and ‘beyond a reasonable doubt,’ where words like that reign every day. That’s where we are going to try this case.”

Heuermann is due back in court on Sept. 27.