Heuermann, 60, has pleaded not guilty to killing four women -- Megan Waterman, Melissa Barthelemy, Amber Costello and Maureen Brainard-Barnes - whose remains were found near Gilgo Beach along Ocean Parkway.
Rex Heuermann expected to be charged with additional murder: reports
Word of the new indictment follows searches by the Gilgo Beach Task Force at Heuermann's Massapequa Park home and a wooded area of Manorville where remains of two women were previously found.
The second search of the Heuermann home focused on the basement.
"They do a nine-day search and then they go back to his house the last week of May and do a six-day search as the Massapequa Park house, so now 10 days later, here we got with an indictment -- a sealed indictment to hopefully be opened Thursday," said ABC News contributor Robert Boyce.
The dismembered remains of Valerie Mack were located in Manorville in November 2000. In July 2003, the dismembered remains of Jessica Taylor were located in the same wooded area.
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"The primary focus again in that basement, in that vault where the guns were kept and also that little room," said Attorney Bob Macedonia, Heuremann's ex-wife Asa Ellerup's lawyer. "I think this time they went back in more with a forensic approach to see if they could obtain any kind of DNA or any kind of forensic evidence linking directly to any of the bodies that had been reported in media as missing over the last 10 to 15 years."
In March 2011, more of Taylor's partial remains were found on Gilgo Beach. In April 2011, more of Mack's remains were discovered -- but she wouldn't be identified until May 2020.
"Looking at these cases and I'm looking at these two ladies now, is this part of that? It seems to be," Boyce said.
Heuermann had been scheduled to appear in court June 18 but is now expected to be arraigned on the new charge Thursday.
"There were a number of investigative steps that were taken. Thursday you'll see the fruits of that investigation," Suffolk County District Attorney Ray Tierney said.