Accused Gilgo Beach serial killer Rex Heuermann appeared in a Long Island courtroom Tuesday with a stone face and a chilling gaze — as prosecutors dumped a “massive amount” of evidence on 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 murder suspect wore a blue shirt, a red tie and a black suit jacket with a pair of khaki pants with grenade pockets on the sides.

His hands were handcuffed in the front.

Heuermann’s hair was matted down and he sported a facial expression that suggested he was annoyed — and at one point scanned the audience with an icy stare, as if looking for someone.

Some of the victims’ relatives were present in court, though Heuermann’s wife, Asa Ellerup — who has said she was shocked by his arrest and 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 brining in an excavator to dig up the backyard in a search for body parts of “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.

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.

She said the case 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 not bed 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 pre-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. In the courtroom we were just in. Where are we have 12 fair and impartial drawers, where we have a fair and impartial judge.

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

Heuermann is due back in court on Sept. 27.