The investigative efforts come just days after Pedro Hernandez, 51, was arrested for the boy's murder, without a body and physical evidence, according to Police Commissioner Raymond Kelly.
"We're in New Jersey talking to a lot of people. Certainly, we're taking to all of Pedro Hernandez's siblings," Kelly said at NYPD headquarters Tuesday.
"We're talking to people who allegedly were there [in the prayer group]."
Hernandez, of Maple Shade, N.J., allegedly told the group in the early 1980s that he had strangled a boy and dumped him in the trash, acccording to the New York Times.
But the leader of the group, Tomas Rivera, said he didn't report the confession to the authorities because "he did not confess to me," the paper said.
The reported decades-old claims could help bolster the case against Hernandez, which appears to hinge on the suspect's confession to investigators last week.
Hernandez's sister, Norma, also reportedly told Camden Police in the mid-'80s that her brother had killed a child, but "nobody did anything about it," according to the Newark Star-Ledger.
The NYPD, meanwhile, is working with the Department of Sanitation to figure out where Patz's body might have been taken after he was killed.
"We are talking to people both in the Sanitation Department and in the private carting industry. There's some issues, obviously," Kelly said. "Records going back that far would not be normally kept in the course of business."
Investigators believe that Hernandez lured Patz, 6, to the basement of the bodega where he worked as a stockboy and then strangled him.
Afterward, he allegedly dumped the boy's body in the trash.
According to Kelly, the department is not yet prepared to go through more than three decades of garbage.
"Obviously, the investigation going forward, it may require that we go to places and execute warrants," Kelly said, "but that hasn't happened."
Sources told DNAinfo that if the boy's body, which was left in a box in an alley on Thompson Street, were picked up by the city's sanitation workers, city officials could likely pinpoint the area where it was buried.
Under that scenario, the garbage would have been taken to the Gansevoort pier on Manhattan's west side and then to the now-defunct Fresh Kills landfill in Staten Island, where it would lay under more than two decades of refuse, the sources said.
But it is also possible that the trash was picked up by a private contractor, which would broaden the possibilities, according to the sources.
Mayor Bloomberg said that he has confidence in the NYPD's investigation.
"I have enormous confidence in the NYPD," he told reporters at an unrelated press conference at Gracie Mansion. "We're trying to do everything as professionally as we possibly can. And there is a lot of evidence that the person of interest here is somebody who certainly had the ability to do it. He was in the right place at the right time.
He's confessed to do it and he's told other people earlier."
Additional reporting by Jill Colvin