Gilgo Beach killings suspect expected to be charged with a 4th killing, source says

LONG ISLAND -- Serial killings suspect Rex Heuermann is expected to be charged with a fourth killing in connection with the Gilgo Beach case, a source familiar with the investigation said Sunday.

Heuermann is expected in court Tuesday, that source and two additional law enforcement sources said. ABC and CBS previously reported the news, citing multiple sources.

Heuermann, an architectural consultant from Massapequa Park, New York, has already been charged with killing three women whose bodies were discovered along a stretch of Long Island's Gilgo Beach in 2010, bound with belts or tape and wrapped in burlap.

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He faces three counts of first-degree murder for the killings of Melissa Barthelemy in 2009 and Megan Waterman and Amber Costello in 2010, according to the Suffolk County District Attorney's Office. He has pleaded not guilty.

"It's bittersweet because I know the details of her death she was just a normal person and that she had a normal, loving heart. Just like any person that you walk down next to on the sidewalk. And she didn't deserve this," said Waterman's sister, Allie Pertell.

The source familiar with the investigation did not make clear which victim Heuermann is expected to be charged in connection with. But authorities have previously said that Heuermann was also the prime suspect in the disappearance and killing of 25-year-old Maureen Brainard-Barnes, whose remains were found near the same location as the other women.

So there's a lot of evidence we had, but they weren't ready to charge. So that was six months into it, a long time for investigators to work at. And apparently, they found the okay, forwarded the case. So they're going forward Tuesday morning," said Robert Boyce, an ABC News contributor and former chief of detectives for NYPD.

The four women, who were discovered within days of each other, came to be known as the "Gilgo Four."

Barthelemy's remains were the first set of female remains found in bushes along an isolated strip of waterfront property in December 2010. At the time, authorities were searching for another missing woman, Shannan Gilbert, a 23-year-old from New Jersey who hadn't been seen since May 2010.

Brainard-Barnes vanished in 2007 and her remains were found in a marshy area near Gilgo Beach three years later. She was wrapped with a belt, which had a buckle bearing the initial "WH," which possibly stand for Hiermann's father, according to ABC News.

CNN has reached out to Heuermann's attorney for comment.

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CNN has reached out to the Suffolk County District Attorney's Office and the Suffolk County Police Department for comment.

Court is scheduled for 9:30 a.m. Tuesday, according to Robert Macedonio, the attorney for Heuermann's estranged wife, Asa Ellerup. The DA requested the date be moved up from a previously scheduled February 6 hearing, Macedonio said.

Ellerup, who filed for divorce last year after her husband was arrested and charged, is expected to attend Tuesday's hearing, Macedonio said.

There are six other women whose bodies were discovered near Gilgo Beach, whose deaths remain unsolved.

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