Since "20/20" appealed directly to you to help solve the mystery of Paul Fronczak, we have been inundated with tips from you. But the two you're about to see which came after this investigation first... See More
Since "20/20" appealed directly to you to help solve the mystery of Paul Fronczak, we have been inundated with tips from you. But the two you're about to see which came after this investigation first aired, have astonished even the FBI. Here's ABC's Brian Ross back at the scene of the crime. Reporter: Until our 20/20 investigation, the case had been as cold as a Chicago winter. But now, in the wake of our first report, the "20/20" tipline has been alive with all kinds of new, and admittedly sometimes whacky leads about the stolen baby or about Paul Fronczak's birth family. Some viewers suggested he might be related to football quarterback Bret Farve. He's not. Others wrote saying he bears a resemblance to the anchorman at our ABC TV station in Indianapolis. Another dead end. And there were at least three 50-year old men who thought they were the stolen baby, based on drawings of what he might look like today. I could be Paul. I might be Paul Fronczak. I do believe that there is a chance of me being Paul Fronczak. Reporter: But while none of those three were a match, we continued to get more tips, including two that got the full attention of the FBI. That hairline is so -- first, a man who grew up in Chicago, with a strong resemblance to the stolen baby. The resemblance is uncanny, if I'm not this guy. Reporter: And then, a surprising admission from a man who believes the stolen baby had been in his home. So you're saying you saw this baby? That baby. Reporter: In your house? And it looks like him, yes. Reporter: The new attention and the new leads grow out of the one, and the only, solid piece of evidence from 50 years ago. The hospital on the south side of Chicago where Paul Fronczak was stolen long since shuttered, its records nowhere to be found. And the key detectives from back then all dead. Do you have any further clues? No sir. Not at this time. Reporter: All that remains is the hospital photograph taken the morning the baby was stolen, at a day and a half old. And that's what was used by the artists at the national center for missing and exploited children to create the age progression images we used in our investigation. I feel good about it. I think it is the ballpark. Yes sir. Reporter: The last known sighting of the baby and the kidnapper was at this intersection in the Chicago neighborhood of Bridgeport where a cab driver told police he had dropped them off after picking them up at the hospital. 35th and Halstead is where the cab came from the hospital. The police went door to door looking for possible suspects. The search went on for days in 1964, hundreds of officers and FBI agents were involved, and our consultant, former FBI agent brad Garrett, says it is likely the kidnapper had some ties here, given past infant abduction cases. They tend to be from the community where they take the child. Reporter: So we did our own door to door canvas, with the image from the center for exploited children, and another one produced by artists commissioned by ABC news from the Michigan firm phojoe.com. Some of the old-timers in Bridgeport remembered the case. I do remember that baby being stolen. They had handbills with pictures of a woman from the newspaper. Reporter: But no one recognized any likeness to the people living around here now. Then last month, Paul Fronczak visited Barbara Walters on "The view." So tell us what your quest is. The main quest is to find what happened to Paul because a tragic thing happened to my mom. The real Paul Fronczak, the real baby who was -- Kidnapped. Kidnapped. Reporter: And a viewer thought she knew the solution to this five decades long mystery, a friend of hers in Dallas by the name of Sam miller. There she sees this picture up on TV, and she called me. She goes, "You're gonna think I'm out of my mind, but you've gotta go to this website and look at this." And so I did, and we all just stood there in shock. Reporter: This is the picture? Yes, it's ghostly to see it in person that large. Reporter: Not only does miller look a lot like one of the age progression images we had produced. But look at the baby pictures. This is the photo taken of the baby just before he was stolen. My -- yeah. Reporter: And your own baby photo from whenever that was taken. It looks like me. And it looks like my son. Reporter: Miller, a 49-year-old Microsoft executive, is the right age to be the stolen baby, grew up in a suburb outside of Chicago, and did not learn he was adopted until earlier this year after doctors told him his kidney disease had taken a serious turn for the worse. He called a cousin for information about the family's medical history. I'm end-stage renal disease, and I need a kidney. She started the sentence with "What kidney disease? You mean you don't know you're adopted?" Reporter: So for miller and his wife and two children, the prospect of finding his real family could be a matter of life and death. So here I am. And hope that I'm able to find a kidney find my family and go on with my life because I'm kind of near the end. Reporter: Miller was eager to provide swabs with his DNA sample to be tested, and made contact with the FBI. This must be quite an emotional moment for you? I look like that guy, and I have no idea where I came from. Reporter: And then as miller was showing me pictures from the family album, the phone rang in the kitchen. It was the call from Chicago he had been waiting for. This is Sam. I would like to know who I am. Reporter: When we return on "20/20". Bowe. ?
This transcript has been automatically generated and may not be 100% accurate.