Transcript for John Walsh returns to TV to help missing children
You can tell that she's not quite the same. We have two parents of a 13 year old who are deceased. We have a 13 year old who was abducted for 88 days against her will forcibly. It doesn't get any more serious than that. Reporter: For 13 year old Jayme Closs, the nightmare, hearing her father shot and watching her mother die. You did cause the death of Denise J. Closs. Reporter: Closs escaped and ran for help. I saw a young woman approach me. She was crying and said I need help, I don't know where I am. I'm lost. Please help me. Reporter: Thin, disheveled but alive. An outcome all too rare. Perhaps no one understands it better than John Walsh. We were holding out hope she was alive. She not only saved herself, she also caught her own perp. In the time she was in there, she found out his last name, what his car looked like. A description, a mazing for a 13 year old. Reporter: His 6-year-old son was abducted. There were no amber alert, no media coverage. I had to beg to get on good morning America. Reporter: They made sure the abduction became national news. But Adam had been murdered. I don't know who would do this to a 6-year-old child. And I said we've got to find your wife and we've got to tell her. And I said you know what? I'll tell her. I'll be the one to tell her. Toughest thing I've ever done. Reporter: The case would remain cold for decades. Walsh turned his attention to making sure no families had to endure what he had. This is America's most wanted. Reporter: Perhaps best known for his work on the show America's most wanted. The next time I see Allen's face, I want to see bars. Reporter: Agencies around the world and the country depended on it. They said John, you have 1422 of the world's most dangerous fugitives, more than any FBI agent in the history of the country, and you're private citizen. Reporter: Over 20 years later his own son's case still unsolved. He called this man to help solve the mystery. In 2008, based on these two pictures and a mountain of evidence, the detectives pieced it together from a different way than the original detectives. The new Hollywood police chief officially closed the case by naming the man who killed him. He would be arrested for the abduction and murder of Adam Walsh on July 27, 1981. It took 27 years to solve that case. Most people don't get that help. Reporter: How often do you think about it? Every day. I'll always be the parent of a murdered child. And it's a wound that cracks over on holidays and birthdays, but I don't bleed to death. I never gave up. And I wanted do honor his memory, and he's my angel. Reporter: After Adam's death, Walsh and his wife became advocates and would help found the national center for missing and exploited children. There are more than 420,000 reports of missing children by law enforcement last year. I believe children are and can be resilient. They have something we don't have. They have this ability to look at the good side of the public. Reporter: But Walsh knows there's still so much danger out there. I'm John Walsh and this is in pursuit. Reporter: He now has a new show, in pursuit with John Walsh on discovery, where he can bring attention to missing children in each episode. This time he's joined by his son Callahan. Your father took us to places. He was our eyes and ears on the ground around the world, now that's going to be you. I spent my time following my dad and being in a family who lost a child, I have empathy for these families. Reporter: In one episode, the story of a 30-year-old manhunt. If he's still alive, he's a horrible creep dirt bag who murdered a very nice young man. He's been out there 30 years. He needs to be brought back to justice. Reporter: What perspective do you think with your youth being a different generation, what will you bring to the show that might be different. This show is, we're harnessing the power of social media, the most important tool is a photo of that child, social media is going to harness the power of the public like the hotline did, and we're going to use it as a tool for our viewers to engage them and give us the tips that we need. Reporter: Walsh knows all too well how important raising awareness can be. He's helped publicize several high-profile cases like Elizabeth smart. The smart family asked me to fly there the day she was recovered. And when I saw Elizabeth walk down the stairs that night, I said this is good. Reporter: And Jaycee Dugard's. It's been exactly six months since the blond sixth grader was kidnapped. Reporter: With Closs's case being the latest to hit headlines, he talks about bus surfers. They'll figure out if that kid goes home alone, if they have to walk half a mile or quarter of a mile. They figure out how they're going to get that kid. It's like hunting. Reporter: What you just said will horrify a number of parents. Because most kids go to school, come home, there's no drama at all. I've been telling parents for years, that the national center has done research the last ten years. The most vulnerable time for a stranger abduction is on the way to school, from the bus stop to school and at night. The bus surfers look for the individual kids that grab their fascination and that they can get the easiest from that bus stop. Reporter: By his own account, John Walsh has spent a lifetime digging, searching the underbelly of society. Seeking not revenge but justice. The problem and the challenge is to keep those kids' pictures and their memory alive. We never give up. I've learned over the years, don't give up. Anything you can do. Reporter: We in America love happy endings. Will Jayme have a happy ending? She's alive. She made it. She made it out. She's not just another picture that we're not going to figure out what happened to her. I hope I get to meet her some day. I'm going to tell her I'm really proud of you. Reporter: I'm Byron Pitts in New York. Our thanks to Byron. In pursuit airs Wednesdays on 10:00/9:00 central.
This transcript has been automatically generated and may not be 100% accurate.