Gregory Wynder, 56, is already doing life in prison for the September 2001 strangling of a woman in her Harlem apartment.
But while Wynder sat in prison, he wrote letters to prosecutors hinting he was responsible for killing two more women, both slain in the South Jamaica home of his girlfriend, Simona Smith.
"That would make it a Norman Bates house," a police source said.
One of Wynder's letters wound up in the hands of Queens detectives, who believe Wynder was writing more than jailhouse fiction.
Detectives and forensic experts from the city medical examiner's office descended on the rear yard of 105-23 170th St. on Wednesday, searching for remains.
That's where Wynder said he dumped, in the 1990s, the brutalized body of Jackie Torres, a homeless woman with whom he had run shoplifting scams, sources said.
Wynder confessed to beating her to death when he thought she had kept some of the loot.
Cops dig up yard in serial-slay probe