ELLENVILLE, N.Y. (CBSNewYork) — Mari Gilbert, the mother of Shannan Gilbert — an escort whose body was one of several found on Long Island’s Gilgo Beach — was found dead in an apartment in Ellenville Saturday, authorities said.

Gilbert, 52, was found dead in an apartment on Warren Street at around 2 p.m., police said.

Gilbert’s daughter, Sarra, 27, was arrested in connection to the incident, police said. She is facing charges of criminal possession of a weapon and murder in the second degree. 

Gilbert is being held at Ulster County jail and is expected to be arraigned on Tuesday.

“Think about it — a mother being murdered by your own child. Can there by anything that you can consider more horrible than that?” family attorney John Ray told CBS2’s Brian Conybeare.

Sarra Gilbert and her mother lived in separate apartments at 9 Warren Street.

“Mari was invited to Sarra’s home and in the living room, she was knifed to death,” Ray said.

Ray said Sarra Gilbert is schizophrenic, has been in-and-out of mental hospitals, and turned violent in recent months, even killing a family dog right in front of her 8-year-old son.

“She drowned the puppy in the presence of her child,” Ray said. “Not so long ago, Sarra purchased a knife at Walmart and took her son into the forest nearby to put him to death. This did not occur because her boyfriend found out about it and put a stop to it.”

The discovery of Shannan Gilbert’s body after her disappearance in 2010 was linked to what became the infamous Gilgo Beach murder investigation, where 10 bodies were found buried along Long Island’s shoreline.

Shannan Gilbert (credit: CBS 2)

Shannan Gilbert (credit: CBS 2)

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.

Gilbert’s official cause of death was classified as “undetermined” back in 2012. Suffolk County police have long held the position that she was not an 11th victim of the suspected serial killer, but fell and drowned in a drug-induced panic in the marsh.

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.

Mari Gilbert was a strong advocate in keeping the investigation into her daughter’s death active, WCBS 880’s Stephanie Colombini reported.

Sarra Gilbert spoke to CBS News three years ago about her sister’s dangerous profession.

“She pretty much thought that, you know, it would never happen to her,” she said at the time.

Officials are expected to hold a press conference on the incident some time this week.