A filmmaker who investigated the Gilgo Beach murders received a "cryptic" message years ago from a mysterious caller who pinned the killings on a Long Island businessman who died by suicide.

"I know who the LISK (Long Island Serial Killer) is or was, and it kind of makes sense that he hasn't killed in quite a while," the message to Josh Zeman said. 

Zeman returned the message by the mystery man, who never gave his name but claimed the killer was James Bissett, the owner of Long Island Aquarium and a significant supplier of burlap sacks in the area. It sparked fringe theories Bissett was involved.

"We really didn't think much of it," said Zeman, who received dozens of messages – if not more – after he tired to lure LISK out of hiding with ads on websites LISK was suspected of frequenting for escorts.

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Rex Heuermann mug shot for Long Island Gilgo Beach murders

Rex Heuermann was charged with murdering three women in New York. (Suffolk County Sheriff’s Office via AP)

"We learned early in the game that LISK, whoever he was, was trolling Backpage.com, Craigslist. He was really active looking for victims. That's how he found the ‘Gilgo Beach 4,’ theoretically," Zeman told Fox News Digital. 

"It was compulsory for him to do that. So, we knew he would be on that to get information. We wanted to lure him out."

VIDEO: MYSTERY CALL TO JOSH ZEMAN IN 2016

Zeman played the voicemail and follow-up conversation with this shadowy caller during his 2016 documentary, "The Killing Season," which he shared with Fox News Digital.

There has been online speculation the voice heard in that call was similar to a voicemail Heuermann left with an interior designer who was in the same Manhattan networking group as Heuermann, which she shared on her TikTok account. 

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Again, Zeman didn't pay much attention to the online rumors, which were debated in forums like Reddit.

"People like to make a lot of connections where there are none," he said. But then Nicole Brass came forward.

VIDEO: REX HEUERMANN'S VOICE MESSAGE TO ACQUAINTANCE 

Brass, a former escort and current hairstylist and makeup artist, told news outlets she believes she went on a date with Heuermann in 2015. 

She said Heuermann repeatedly talked about how he was a true crime fan and specifically mentioned the Gilgo Beach case and how the burlap sacks that the victims were wrapped in were traced back to Bissett.

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"He was like, ‘You know it could be Bissett, the aquarium owner,’" Brass told Lauren Matthias, host of the "Hidden True Crime" podcast. "What weirded me out the most was that he's saying all this and being real creepy about it and then says, ‘I live right by Gilgo Beach.’"

Matthias asked Brass if she thought it was an attempt to mislead her or intimidate her.

"I feel like he wanted to brag about what he had done but couldn't," Brass told Matthias.

James Bissett

James Bissett, the owner of Long Island Aquarium who died by suicide in December 2011, was a fringe suspect mostly connected by theory to the Gilgo Beach case. But his name was brought up twice, once by a mystery caller in 2016 to a filmmaker and again to a woman Gilgo Beach suspect Rex Heuermann went on a date with in 2015.  (Obituary )

Bissett was targeted by police as a person of interest, but his name quickly faded. 

He was never charged or publicly tied to any of the deaths by authorities. So, mentioning his name again piqued Zeman's curiosity.

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"When I heard the name Bissett and that Rex Heuermann said to (Brass), ‘Bissett,’ that suddenly made me question if it could be him (who called in 2016)," Zeman said. 

Some sleuths and people interested in the case say the voices are similar. Others point out differences as they slowed both recordings and listened carefully.

Police at Giglo Beach serial killer's house

Police use ground-penetrating radar to search Rex Heuermann’s house in Massapequa Park, N.Y., Sunday, July 23, 2023. (Mega for Fox News Digital)

The jury is still out, even for Zeman, on whether he actually spoke to Heuermann, but it's possible, he said.

In 2016, when "The Killing Season" originally aired, it was the only major documentary at the time about the LISK. After Heuermann's arrest this month, prosecutors detailed over 200 of Heuermann's alleged Google searches. 

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That seemed to show his almost obsessive interest in the case. 

"If he was out there looking for information, which we know through his Google searches that he was looking up podcasts and documentaries and very invested in knowing what was going on in the case and knowing how close the police were," Zeman said. "It really wouldn't surprise me that if he suddenly saw a post on Backpage and actively soliciting sex workers … that he would call and kind of throw us off his tracks."

Google searches

Rex Heuermann's alleged Google searches (Suffolk County DA)

Charges against Rex Heuermann

As it stands now, Heuermann is accused of killing Melissa Barthelemy, 24, Megan Waterman, 22, and Amber Lynn Costello, 27, and is the prime suspect in 25-year-old Maureen Brainard-Barnes' murder.

He was charged with six counts of murder (first- and second-degree for each victim), and pleaded not guilty to all charges. 

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Prosecutors haven't said whether they believe Heuermann is connected to six other victims on Gilgo Beach.

But his arrest prompted law enforcement agencies across the country, including in South Carolina, Las Vegas and Atlantic City, to reexamine missing persons cases and cold cases to determine if Heuermann was involved.