ELLENVILLE, N.Y. - The mother of a woman who was found dead at Gilgo Beach was killed Saturday, and her other daughter is charged with second-degree murder, police say.

Mari Gilbert, mother of Shannan Gilbert, was killed in Ellenville, Ulster County.

Police say 52-year-old Mari Gilbert was stabbed repeatedly by her daughter, Sarra Elizabeth Gilbert, 27, but they are not releasing a motive. Another daughter initially called police to Sarra's apartment to check on their mother.

As News 12 has reported, Mari Gilbert had been fighting to find out how her daughter died back in 2010. The body of 24-year-old Shannan Gilbert was found near Gilgo Beach and led to the discovery of 10 sets of human remains in the area.

The original autopsy conducted in the case ruled that Shannan Gilbert's cause of death was undetermined, but the family had an independent autopsy performed that said she may have died of strangulation.

The Gilbert family's attorney, John Ray, says Sarra Gilbert has a history of schizophrenia and has been in and out of mental facilities for years. She recently drowned her own pet puppy in a bathtub in front of her son, Ray says.

Sarra Gilbert is now being held without bail on the murder charge. Ray says that if he represents her, he will use an insanity defense.