Suspected Gilgo Beach serial killer Rex Heuermann will make a surprise return to court Tuesday, weeks before his next scheduled hearing, and investigators on a task force dedicated to cracking the case are expected to announce a "significant development."

Sources tell Fox News Digital the New York City architect is expected to face charges for a fourth murder after a new indictment is unsealed at the 9:30 a.m. hearing.

Suffolk County District Attorney Ray Tierney's office said the Gilgo Beach Homicide Investigation Task Force will hold a press conference immediately following the hearing, with speakers including the DA, Sheriff Errol Toulon Jr. and acting Police Commissioner Robert Waring.

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Police arrested Heuermann outside his Manhattan office in July in the cold case murders of three other women, Melissa Barthelemy, 24, Megan Waterman, 22, and Amber Costello, 27.

Hair DNA found in the burlap sack containing Waterman's remains matched a sample that police collected from a discarded pizza box outside Heuermann's Manhattan office, according to prosecutors.

Tierney said after the arrest that Heuermann was investigators' "prime suspect" in at least one more murder, the slaying of Maureen Brainard-Barnes, 25, whose remains were found near the others.

Charges were expected eventually as investigators continued to work the case.

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In 2010, a woman named Shannan Gilbert placed a panicked 911 call to county police, then vanished. Police began searching the area and recovered 10 sets of remains before finally finding hers, including those of the "Gilgo Four," four young women who were discovered in proximity to one another under similar circumstances.

Police now say Gilbert's death was an accident, but the attorney for her family, John Ray, has disputed that claim. 

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Since his arrest, Heuermann has been held without bail at the county jail in Yaphank, where he has been trading letters with the convicted "Happy Face" serial killer Keith Jesperson and was briefly on suicide watch.

Before his arrest, prosecutors said they found evidence showing he was closely following news about the Gilgo investigation and continued to patronize sex workers, his suspected prey of choice.

"He was searching, compulsively searching pictures of the victims, but not only pictures of the victims, pictures of their relatives, their sisters, their children, and he was trying to locate those individuals," Tierney said over the summer.

Heuermann was born and raised in Massapequa Park, New York. He bought his childhood home from his mother in the 1990s and moved his own family there. His wife filed for divorce shortly after the arrest.

Neighbors described him as quiet and unassuming, but some said they got creepy vibes from the unkempt home, which has aging siding, twisted flashing along the roof and two-by-four lumber holding up the front awning.