happiness. Petsmart??. From his home in Las Vegas, a city defined by luck and lust, Paul Fronczak took the biggest gamble of his life. After decades of wondering, of suspecting that he might not be the... See More
happiness. Petsmart??. From his home in Las Vegas, a city defined by luck and lust, Paul Fronczak took the biggest gamble of his life. After decades of wondering, of suspecting that he might not be the baby stolen from his mother's arms, he asked his parents for samples of their DNA. I think I got them off guard a little bit, because I, I had just, I mentioned my, to my mom, did you ever really wonder if I was really your child? She said, yeah, we, we thought about it. I said, well, what if we can find out? A way? And they said, well, yeah, we'd like to know. And then I went and got a DNA kit, and it was all done in five minutes. Reporter: But later, second thoughts. Were you ready to handle whatever secrets might come out? Yes. Were your parents ready to handle the secrets? No. They called me and they said, "We don't want you to have that test done, and if you do it, we don't want to know." I had the packet ready to go on my desk in my house for about three weeks, and I would pass it every day, fighting with whether to do it or not. And finally one day I told my wife, I said, you know what, I have to do this. I really need to know. Reporter: It was the answer he had anticipated and feared. The results were in. The test that would tell him if he'd been living a lie. Describe the moment when you got the results of the DNA test. I got the phone call, I found out there is no remote possibility that I was a Fronczak child. All the sudden I felt the color drain from my face. And I said, "Are you okay?" And he said, "I don't know." He said, "I feel a little dizzy. I need to stay in my chair right now." All the sudden I started thinking, I don't know anything about myself. I don't know how old I am, my heritage, my birthday, every, all these things that people take for granted, I, everything I thought was my life wasn't. He said, "I don't know anything about myself." And I said, "Well, you do. You're -- you're my husband, you're Emma's dad. You know who you are. Reporter: But who he is is not this baby boy. For Chester and Dora Fronczak the fairy tale ending to their family tragedy was revealed to be just that, a fiction. How does a loving son say to his parents, you are not my biological parents? That was another hurdle I had to go through. My dad is 82. He has a hard time hearing on the phone, and my mom, I knew she would be very upset. So, I really through the best way would be to send them a letter. Would you read it? Sure. So it's dear, mom and dad. First, I am your son and always will be. I love you both, and that will be forever. I am not the kidnapped baby that you had stolen from your arms on April 27th, 1964. This means that the real Paul Joseph Fronczak may still be out there, alive, not knowing who he is. I know this is hard for you, but this is also about me at this point. What was the reaction of your parents? My dad called me, and he called me a name that he never has called me before in my life. How did you feel? I was speechless. And then my dad hung up. In their heart, I was their son, and -- and that's all that mattered. Did you think maybe you shouldn't have taken the DNA test? I struggle with that quite a bit. It's, I mean, I love my parents, and I always do what they ask. But this is something that I really felt I had to do. But the truth hurts. The fronczaks' prayers to find their stolen baby had actually never been answered. Paul's fond memories have become bittersweet, tainted by the knowledge that he was not kidnapped and found. He had been abandoned, most likely by a parent. The toughest moment for me, and I watch the home movies and I see a young boy running around that someone had just left. It kills me every time I see that. I look at my daughter. She's 4 years old. The thought of leaving her behind, that's what really hurts me the most. Paul is now determined to solve the two mysteries in his life. Who is he, and what happened to his parents' stolen baby. My main goal is to find the real Paul. My parents raised me and they did a great job. I feel if I can't do anything I can to help them find their real child. I'm not doing my job as a son. Reporter: Don't you want to find out who you are? It would be a bonus. Reporter: To help Paul solve these miseries we introduced to to to our NBA profiler. I'm in this for the long hall. I'm in Chicago -- Asking callers to send in tips. If you know anything about the case. Let us hear from you. Coming up. Shocking tips. The resemblance is uncanny if I'm not this guy. This is what the baby would look like today. Is he the real Paul? Next at "Stolen at birth."
This transcript has been automatically generated and may not be 100% accurate.