"20/20," "Stolen at birth" continues. Once again, Barbara Walters. Reporter: For Paul Fronczak, a mission has become an obsession. Between breakfast and ballet lessons he's on the hunt. I work a... See More
"20/20," "Stolen at birth" continues. Once again, Barbara Walters. Reporter: For Paul Fronczak, a mission has become an obsession. Between breakfast and ballet lessons he's on the hunt. I work a full-time job, I have a family, but this, this is my life. And this is my only shot at solving these mysteries. So I put as much time as I -- as I can. Everyone goes to bed at night, I'm, I'm on line researching. This is my first actual baby picture right here. Reporter: His focus is finding his parents' stolen baby. But he is still searching for clues to his own identity. I feel kind of like an imposter because I am still using his birth certificate. Paul is out there, and I have his birth certificate and I want to give it to him and I want to find mine. Reporter: Desperate to find any connection to his biological family, Paul sent DNA samples to three genealogy sites: 23 and me, family tree DNA and ancestry.com. We took the sample that you gave us and we put it on a chip, and what that does is it gives us a unique DNA signature that only you have. So we compare your DNA to DNA from populations all over the world. So, you're kind of like csi but you work with DNA? It's family history. Reporter: The results were Paul's first indication of who he is and where he's from. There were surprises about his ethnic roots. You are, uh, 37% according to our analyses, of european-jewish descent. Wow. Is that new? Well, I was raised a Roman catholic. Well, uh -- So this is interesting. I've been twice baptized and I'm actually jewish. So, it's kind of cool. I have to learn a whole new religion now. I'm excited about that. Reporter: Even more exciting, a major development in ancestry.com's search. All of a sudden this name pops up and it says possible third cousin. Finally a clue. And for Paul a chance to meet his first blood relative. Her name, Fran Kirby. It's a moment 50 years in the making. I'm very excited. You get excited, you get nervous, how is this person going to react to me reaching out to them, what's the response going to be? Well let's find out the response. We have brought here to meet you, your cousin Fran. Reporter: The first branch in Paul's family tree blossoming into the ordinary miracle of a family reunion. Hi. Hi, Paul. Nice to meet you. Cousin Fran. A blood relative. How's that feel? It feels pretty good. Did you know that Paul existed? No, I didn't. I googled after I found out, I found out the whole story, and saw your "20/20" Paul, just to find out that there might be a relative is a very big deal for you, isn't it? It's a very big deal. So this is really huge, this is one step closer. Reporter: But then another step --make that a leap, closer. Paul got another match on ancestry.com, this time a possible second cousin. Reporter: Finding a second cousin match is substantially better than finding a third cousin match. For cece Moore, a genetic genealogist helping Paul with his case, it was a eureka moment. I was extremely excited. I thought we might be able to have a very quick resolution to this case. Reporter: That cousin's name, Alan Fisch, a 57 year-old father from New York. A second cousin could unlock the mystery. Alan and Paul's parents could be first cousins, their grandparents siblings. But there is one ironic obstacle. Turns out, Alan was himself adopted. So just like Paul, he was searching for his biological parents. To find that his closest match turns out to be adopted was just unbelievable. Incredibly disappointing. It just couldn't be an easy case, could it, Barbara? No, exactly. Reporter: A setback, and then a tragedy. Days before Alan would see court records revealing details about his birth mother, he died of a sudden blood clot. Alan's children and widow Randi are determined to carry on Alan's search and help Paul with his. It's nice to meet you. Hi. We know this must be very difficult. In this very sensitive time, you still came in to meet Paul and help him on his journey. Yes. Why did you want to do this? All four kids at the same time said they wanted to honor Alan's memory and finish this. He was so excited to meet you. To have this happen, my father passing away just days before he meets him is just, it's surreal. I can't, can't believe it. Was your husband very curious about Paul? Yes. What did he want to know? He wanted to know everything about him. This is amazing. And thank you for continuing this. Because it's going to be an interesting journey. Reporter: The next step in that journey, tracking down Alan's birth mother. This week, with "20/20's" help, the family got her name. Age 15. Born November 15th, 1940. If found she would be Paul's closest relative so far. Paul's hope is that every clue brings a tragic mystery closer to being solved. Look at all these people. This is all of your family. Are you getting to be more hopeful that you'll find out who you are, who Paul Fronczak is, the whole story? If it's possible to me more hopeful, because I'm really, really a hopeful guy. You know? I still think we're going to solve both these mysteries. Wouldn't that be great? Yes. It's going to happen. On the eve of the St.
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