For years, Mari Gilbert insisted the death of daughter Shannan — a Jersey City prostitute — in a Long Island beach community in 2010 was the work of a serial killer, perhaps the same one who left 10 other sets of human remains along a remote stretch of beach highway, just miles from where Shannan Gilbert's body was found.

Mari Gilbert would occasionally appear in public with her attorney and surviving daughters to plead their case, most recently at a press conference last winter where they pointed to an independent autopsy suggesting the 24-year-old had been strangled, contrary to a medical examiner's inconclusive findings and police theories that the young woman drowned.

Now, the soft-spoken mother who worked at Wal-Mart herself is dead, and authorities say another of her daughters is the one who violently stabbed the 52-year-old woman to death in upstate New York.

"There's been too much death, too much anger and too much tragedy here," one of Mari Gilbert's attorneys, Vesselin Mitev, said after authorities announced the arrest of Sarra Gilbert, 27, in the Saturday killing of her mother.

Gilbert, who suffers from schizophrenia and other mental issues, according to another family lawyer, is being held without bail on murder and other charges.

That attorney, John Ray, said not only does he intend to defend Sarra Gilbert — offering a possible insanity defense — but he will press on with Mari Gilbert's quest to get to the bottom of the Shannan Gilbert mystery.

She disappeared in May 2010 after meeting a client for sex in the exclusive beachfront community of Oak Beach, about 15 miles east of Jones Beach.

A K-9 officer and his cadaver dog were on a training mission searching for Gilbert in December of that year when they happened upon what would become, by spring of the following year, 10 sets of human remains — eight women, a man and a toddler. The remains were found strewn along several miles of thicket adjacent to Ocean Parkway, just east of Jones Beach.

It took until December 2011 before Shannan Gilbert's skeletal remains were located — about three miles west of where the others were found. At least four of the other women were identified as prostitutes; others included a man and a young child.

No suspect has ever been identified by police in any of the cases.

Police and prosecutors have said they don't think Shannan Gilbert was the 11th victim and suggest she accidentally drowned. Mari Gilbert insisted they were wrong.

The family got noted forensic pathologist Dr. Michael Baden to conduct an independent review. He found earlier this year that while "there is insufficient information to determine a definite cause of death," the autopsy findings "are consistent with homicidal strangulation."

The Suffolk County Police Department, which is responsible for investigating all the killings, has gone through several changes in leadership in the years since the case first broke. Earlier this year, Police Chief James Burke pleaded guilty to federal charges in the assault of a suspect who had broken into his police vehicle.

After his arrest, the department brought in the FBI to assist with the serial killer case, a change from the previous leadership's aversion to working with them, Commissioner Timothy Sini said.

He said the FBI has helped with psychological profiles of possible killer or killers, and is assisting in other ways. He declined to comment on whether it has produced any leads or suspects, but said any time the case garners fresh media attention — like the death of Mari Gilbert — the department sees a spike in tips to its hotline.

He said the police theory remains that Shannan Gilbert likely drowned, but that investigators were keeping an open mind.

In the meantime, the Gilbert family attorney says they will press on to find the culprit they believe killed Shannan and the others. "This motivates us to work even harder," Ray said.

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