Now, to an abc news exclusive. A truly remarkable story. The fbi is, in fact, looking for your help this morning. Reopening an almost half-century-old mystery. Kidnapping and mistaken identity. A... See More
Now, to an abc news exclusive. A truly remarkable story. The fbi is, in fact, looking for your help this morning. Reopening an almost half-century-old mystery. Kidnapping and mistaken identity. A remarkable story coming to light thanks to months of work by our barbara walters. Barbara here with us this morning. And this all started when a newborn was stolen from a hospital in chicago. That's right. And by the way, you mentioned my colleagues. This is the abc investigative unit. And we're very big. Imagine a mother whose baby is stolen out of her arms. She gets the baby back. Or so she thinks. And now, almost 50 years later, that son she raised has come forward to speak exclusively to us. Looking at old family photographs of paul fronczak is a strange experience. Because the baby in his baby pictures is not him. How do you feel when you see this picture? I feel like I want to find him and hug him and make sure he's okay. Reporter: Paul fronczak recently discovered his entire life, his name, his parents, his birthday, all of it, is a big mystery. A mystery that began with a kidnapping 49 years ago, in 1964. Just a day after paul fronczak was born. The first child of chester and dora fronczak. But baby paul was snatched from his mother's arms, right in the maternity ward of a chicago hospital.Baby was kidnapped. The baby was gone. I don't think I could take another woman's baby. Reporter: Her public appeal to the kidnapper went unheeded. We are questioning suspects. Reporter: A massive dragnet came up empty. Just over a year later, a child somewhat matching paul's description was found. You are discovered in a stroller in newark, new jersey. Abandoned in a stroller in a blue suit. Reporter: The fronczaks claim the little boy in a blue suit as her own. Now an adult, paul works for a college in nevada. He's married and has a child of his own. A normal life. Until a year ago, when a dna test showed he is not the fronczaks' child after all. Now that you know the truth, that you are not the real paul fronczak, what are you trying to accomplish? My main goal for this whole project is to find the real paul. My parents raised me. And they did a great job. And I feel that if I don't do everything I can to help find their real child, then I'm not doing my job as a son. And you just mentioned it. Paul fronczak wants to find paul fronczak. The real paul fronczak. Who is he? Why did he, after all these years, get that dna test? His parents didn't want it. They wanted to just -- you know, you're our son. Let sleeping dogs lie. He always knew that he was different. He has a brother. The true son, the biological son of the fronczaks. He knew he was different. And he had to find out why. It's not just a search for him. It's a search for himself, as well. The fbi has reopened this case. Is paul the man we know, the man we saw you interview, is he hopeful this will be concluded, resolved in some way? What he said to me is I am cautiously optimistic. What he wants from everybody else, is that if you know anything about him, any of you watching or any of you know anything, please let us know because he hopes that he will know more when this information is discovered. And also, all of the abc unit is working on it. So, we're going to investigate. We hope we will find it out. A full report will be out in the fall. This is a mystery within a mystery. This is a "20/20" I'm not going to miss. Thank you so much, barbara. Again, if you have any tips or clues that can help solve this case, go to goodmorningamerica.Com on yahoo! Send them to us now.
This transcript has been automatically generated and may not be 100% accurate.