Mari Gilbert, mother of a sex worker whose disappearance led to the discovery of a serial killer's Long Island mass grave, which was filled mostly with slain prostitutes, died on Saturday. Upstate NY police arrested her daughter Sarra Gilbert, who was charged with murder.

Jersey City resident Shannan Gilbert, 24, went missing, last seen running from a client's home, in May 2010, and, during the search for her, investigators ended up finding 10 bodies in Gilgo Beach over many years. While authorities believe that one person is behind the deaths of the prostitutes, they say that Shannan Gilbert's death is unrelated to the serial killings.

Mari Gilbert, 52, who Newsday describes as "a vocal advocate for her daughter after Shannan’s death," apparently went to daughter Sarra Gilbert's home in Ellenville, where she was fatally stabbed.

The family's attorney in lawsuits related to Shannan Gilbert's death told Newsday that Sarra Gilbert had been 'hearing voices for several days" and didn't believe that she was competent, adding she was "not in control of her own faculties."

Earlier this year, Mari Gilbert demanded that the police take her daughter's murder seriously: "This is my daughter Shannan. She was not perfect. No one is perfect. But she was loved. She was cared for. She does not deserve to be forgotten." She also told Newsday, "I was very angry, as any parent should be, but as time went by I kind of realized that maybe that was her destiny to help other families."