(CHICAGO) -- The FBI is working several "solid new leads" in the unsolved case of a baby stolen from his mother's arms almost 50 years ago in Chicago.
Authorities had closed the case in 1966 after the parents, Chester and Dora Fronczak, identified an abandoned infant in New Jersey as their son Paul.
This year, the FBI re-opened the investigation after DNA tests revealed that Paul was not the Fronczak's biological son.
"We're going to do everything that we can to follow up to see if that baby is out there," said Bob Shields, the special agent in charge of the Chicago FBI office.
In an interview to be broadcast Friday on an ABC News 20/20 report, along with other new details in the Paul Fronczak case, the FBI's Shields reveals that a team of agents is actively following the new leads that have developed in the wake of previous stories by ABC News and other news outlets.
At least four individuals have come forward to claim they could be the stolen baby, after seeing age-progression images broadcast on ABC News.
All four men are 49 or 50 years old, in the range of the age of the stolen baby who was born in April, 1964.
One of the four men, living in Kansas City, contacted both ABC News and the FBI to offer a DNA sample to be matched with the elderly Fronczak parents or their biological son David.
The FBI's Shields says he hopes more leads will develop following the Friday 20/20 broadcast.
"We believe there's someone out there that has information," Shields told ABC News. "We want to find that child but we also want to find the person that took the child."
Tune into 20/20 Friday at 10 p.m. ET for the full ABC News report.
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