Mental illness drove Sarra Gilbert to kill her mother, Mari Gilbert - five years after Sarra's sister was found dead near a suspected serial killer's mass grave in Long Island, New York - Mari's lawyer and others close to the family allege to People. "It was schizophrenia," attorney John Ray, tells People. "Sarra was hospitalized several times. Over the past couple of days she began to hear voices. She called her mother and said come over. ... And she stabbed her to death." Police say Mari's body was discovered in her daughter's home in Ellenville on Saturday. They arrested Sarra later...