MINEOLA, N.Y. (CBSNewYork/AP) — An attorney says the death of a New York woman won’t end the quest to confirm her suspicions that her daughter was a homicide victim.

Mari Gilbert, 52, was stabbed to death in upstate Ellenville on Saturday, but family attorney John Ray vowed he’ll continue to seek answers in her daughter’s death.

Shannan Gilbert was a prostitute whose 2010 disappearance led to the discovery of 10 sets of human remains along a Long Island beach highway, in a case that became known as the Gilgo Beach murders.

The first body was found on Dec. 11, 2010 while police were searching for Gilbert. By April, police had discovered the sets of 10 remains on Gilgo Beach, all found about seven miles apart along Ocean Parkway. Shannan Gilbert’s remains were found on Dec. 13, 2011 in a marshy area on Oak Beach about a quarter-mile from where her cell phone, purse, jeans, shoes and lip gloss were found the week before.

“If not for Shannon Gilbert, the killing field would lie fallow and no one would’ve known about it,” Ray said.

Gilbert’s official cause of death was classified as “undetermined” back in 2012.

“I believe the police at first dismissed her. It took this long to search for her? And if we weren’t on the phone, they may not have searched at all,” Mari Gilbert told CBS2 previously.

Police and prosecutors have said they don’t think Shannan Gilbert was the 11th victim of a serial killer and they think she accidentally drowned. Mari Gilbert insisted they were wrong.

Police allege Mari Gilbert was killed by another daughter, 27-year-old Sarra Gilbert, who is facing charges of criminal possession of a weapon and murder in the second degree.

Police Chief Phillip Mattracion said officers found Mari’s body with multiple stab wounds, a knife nearby and Sarra standing in the kitchen with blood on her clothing.

“He observed the daughter Sarra Gilbert in the kitchen,” Mattracion told CBS2’s Lou Young. “She had blood on her clothes. The official cause of death is listed as multiple stab wounds.”

Ray said Sarra Gilbert hasn’t been the same since her sister’s body was discovered and suffers from mental illness.

“Sarra had been acting in irrational ways and she had actually been hearing voices, and these voices were telling her what to do,” Ray said. “She’s been hospitalized various times over the last year for her psychiatric condition.”

Sarra Gilbert is expected to be arraigned on Tuesday.

“This is truly a tragedy — a great, horrible tragedy of American motherhood,” Ray said.

Shannon Gilbert’s estate is suing former Suffolk County police surgeon Dr. C. Peter Hacket in connection with her death — he owned a house on Oak Beach.

Mari Gilbert had custody of Sarra Gilbert’s child. He is now with his father.

Sarra Gilbert’s lawyer hasn’t commented.

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