Garrido was convicted of kidnapping and repeatedly raping Katie Hall in a Nevada storage unit in 1977 and served more than 10 years of a 50-year sentence before he was paroled. He is also considered a suspect in two other missing child cases, the 1988 abduction of 9-year-old Michaela Garecht and the 1989 disappearance of 11-year-old Ilene Misheloff.
"[Garrido's] a guy that should've never been out there, that's the guy we need to track. That's the level-three violent sex offender that everybody needs to know is next door," Walsh said. "It's not about civil liberties. I grew up in the '60s. I believe in civil liberties, and I believe in America. But I believe that once somebody demonstrated that they're an animal, that they've crossed that line, that they've hurt a woman or a child, then you need to track them."
On the set of his show, Walsh often invites victims' family members to the taping. When he meets parents who have lost their child, he said the pain of losing Adam hits him again.
"I look at this woman and see the pain and the tears in her eyes and say, 'I know where she is at.' She says, 'How could this happen to me? How could I be in this place?' And you really don't have the answer, I still don't have the answer," Walsh said. "I am still heartbroken…and you're wounded, but you will survive. You will go on; you go on and do the best you can to deal with it."
Walsh bonds with the families -- but none more so than the Smart family from Salt Lake City. When their 14-year-old daughter, Elizabeth, was abducted from her bedroom in 2002, Walsh did six shows on her case.
Nine months after Elizabeth Smart was abducted, an elderly couple, who had heard about the smart case on "America's Most Wanted," spotted a man traveling with two companions -- and one of them was a disguised Elizabeth Smart.
"I think the highlight of the 23 years is when the Smart family asked me to fly to Salt Lake City the day that Elizabeth was recovered because we never gave up and Ed and Lois never gave up," Walsh told "Nightline."
"And when I saw Elizabeth walk down the stairs that night, I said, 'This is good, this is a home run.'"
Just last month, Elizabeth Smart, who is now 21, came face to face with her alleged abductor, Brian David Mitchell, in court.
Speaking for the first time, Smart testified that she was raped "on a daily basis up to three or four times," while in captivity for nine months. She testified as part of the proceedings to determine Mitchell's mental competency, in the hope that he can stand trial and that justice will finally be served.
Justice is what had also eluded the Walsh family for decades. But last year, Chad Wagner, a new chief of police in Hollywood, Fla., closed Adam's case, officially declaring that Ottis Toole, a convicted pedophile and serial killer, murdered Adam in 1981. It was an emotional moment for Walsh and his family.
"For 27 years, we have been asking who could take a 6-year-old boy and murder him and decapitate him. Who? We needed to know. We needed to know. And today we know," Walsh said at a news conference.
Walsh told "Nightline" that by declaring Toole the murderer, "justice was served."