Rex Heuermann's arrest in Long Island's infamous cold case is a "good first step," but it's "just the tip of the iceberg," a documentary filmmaker and lawyer told Fox News Digital in separate interviews. 

Heuermann, a 59-year-old married father of two and an architect working in Manhattan, allegedly killed three of the four women known as the "Gilgo Beach 4," and he's the prime suspect in the fourth woman's death.

But there were at least six more bodies found in the same area of Gilgo Beach that can't be forgotten, said John Ray, a lawyer who represents the families of Shannon Gilbert and Jessica Taylor. 

Heuerman's arrest "is just the tip of the iceberg." Ray said. "What's below the surface are more murders which aren't accounted for yet, including Shannon and Jessica, and we can't forget them."

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Victims with connections to Long Island, New York's Gilgo Beach

Maureen Brainard-Barnes, Melissa Barthelemy, Megan Waterman and Amber Costello were known as the "Gilgo 4." The discovery of their bodies led to other gruesome discoveries victims in the area. 

Gilbert's May 2010 missing person case and subsequent search along Ocean Parkway on Long Island led law enforcement to find the remains of the "Gilgo 4" within a quarter mile of each other in December 2010. 

Josh Zeman, a director and producer who created the eight-part documentary "The Killing Season" in 2017, told Fox News Digital that he "never thought he would get to this day."

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"This is at least a first step, but there are so many more victims out there," said Zeman, who attended Friday's press conference. "There were a number of bodies found along Gilgo Beach. There's the ‘GB 4’ and then there are other victims that were dismembered. 

"So the arrest brings up this big question. Is it just the ‘GB4,' the ‘Gilgo Beach 4,' or does it go beyond the other killings? And that, I think, is really the big question."

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There's been speculation and rumors around this case, Zeman said. "People have always wondered whether it was one killer or two. Obviously, the idea that there are two killers roaming around and using the same dump site is really disturbing."

The question was posed to Ray, who said he doesn't know if Heuermann is involved in his clients' cases or if there's someone else, at this point. Heuermann was someone not on his radar before the arrest, he said.

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Jasmine Robinson, a family representative for Taylor, said in a statement that she’s "hopeful for the future and hopeful that a connection is made" to resolve the other cases.

As it stands now, on Saturday evening, Heuermann is accused of killing three of the four "GB4" victims - Melissa Barthelemy, Megan Waterman and Amber Costello - although he's the prime suspect in Maureen Brainard's death as well.

Alleged Gilgo Beach serial killer led into court

Rex Heuermann is led into Arthur M. Cromarty Criminal Complex in Riverhead, NY on Friday, July 14, 2023. The 59 year old is being charged with three counts of murder in relation to the deaths of victims found on Gilgo Beach. (Matt Agudo/Splash for Fox News Digital)

More charges could be added, according to authorities. 

Heuermann was officially arrested and booked Friday on six counts of murder (first- and second-degree murder for each of his alleged victims), and he pleaded not guilty to all charges. 

READ: CASE AGAINST REX HEUERMANN

His lawyer, Michael Brown, said the evidence against his client is "extremely circumstantial" and told reporters that Heuermann repeatedly said, "I didn't do this," through tears. 

Brown was given the case Friday, so he's reviewing the evidence and couldn't comment on specific allegations. 

Gilgo Beach murders victims Amber Costello, Maureen Brainard-Barnes, Melissa Barthelemy, Megan Waterman

Gilgo Beach murders victims Amber Costello (top left), Maureen Brainard-Barnes (top right), Melissa Barthelemy (bottom left), and Megan Waterman (bottom right). (Suffolk County Police Department)

Since Heuermann's arrest, Ray has been interviewed by several news outlets, and pushed Suffolk County District Attorney Raymond Tierney to continue the investigation to get justice for the other victims.

"We're hoping that the police don't rush to be content with their victory, but instead that they move ahead, and with the same enthusiasm," Ray said. 

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Both Ray and Zeman praised Suffolk County District Attorney Raymond Tierney, who put together a multi-agency taskforce "with each agency's top personnel" when he took office in 2022. 

They zeroed in on Heuermann in March 2022 because of his truck and built the case from there without tipping him off, DA Tierney said on Friday. 

"Seeing the evidence that the Suffolk County Police Department, Rodney Harrison had put together, I was extremely impressed with the work that they had done," Zeman said.

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The Gilgo Beach murders have remained unsolved more than a decade after the search for missing escort Shannan Gilbert, 24, first led police to the bodies of multiple sex workers and other victims east of New York City. 

Separate from the "Gilgo 4" include the partial remains of 20-year-old Jessica Taylor, which were found in March 2011 Near Gilgo Beach. Authorities said part of Taylor’s body was discovered eight years earlier and 40 miles away in Manorville, New York.

Gilgo Beach murders map

The locations where eight of 10 bodies were found near Gilgo Beach since December 2010 are seen in this Suffolk County Police handout image. (Reuters/Courtesy of Suffolk County Police)

Days later, three more sets of human remains were discovered alongside Ocean Parkway. The first was 24-year-old Valerie Mack, whose partial remains had also been found in Manorville years earlier.

An unidentified toddler was found near Mack, according to the official website dedicated to the case.

Two miles west, police discovered the skeletal remains of an unidentified Asian man — or transgender woman — believed to be 17 to 23 years old.

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A week later, in April 2011, two more sets of partial remains were found along Ocean Parkway. The first were those of the woman known as "Peaches," believed to be the mother of the toddler found the week before. 

Part of her body had been previously discovered in Hempstead Lake State Park in 1997. The second was the skull of a woman who was linked to remains found on Fire Island in 1996.