NEW YORK — When he started "America's Most Wanted," John Walsh could point to at least one thing in its favor: Society's swampland of bad people doing bad things would never run dry. On that basis, the show seems a cinch to run forever.

It recently marked 20 years on the air. And this week it observes another milestone: The arrest of the 1,000th fugitive targeted by "AMW" since April 1988 — Dwight Smith, a New York real estate agent accused of murdering a friend over a deal gone awry.

Smith was on the lam for nearly a year. Then, on April 19, an anonymous caller who had recognized him on the "AMW" Web site disclosed his whereabouts: an address in Richmond, Va. That night, Smith was in police custody.

Airing from Times Square, this special edition of "AMW" may have a more festive feel than usual (especially since the show has logged 21 more captures in the meantime). But Walsh is under no delusions the larger fight is over, or will ever be won.

"I know firsthand that lots of people get away with murder," he states flatly.

He found that out when his 6-year-old son Adam was abducted and murdered in 1981. The investigation was botched. No one was charged with the crime. The likely killer died in prison, where he was serving time for an unrelated crime. Adam got no justice.

"But on 'AMW' I see some incredible, immediate results," Walsh says, "where you really do catch somebody. Get some justice. And maybe save lives: You know, some killers are gonna continue until they get caught."

A former Florida hotel developer, Walsh, 62, has spent a quarter-century as a crusader for tougher laws against sex offenders, more cooperation among law enforcement agencies, and citizen involvement in flushing out fugitives.

"Now, join the manhunt!" exhorts a husky-voiced announcer at the top of "America's Most Wanted," which keeps its 6.2 million viewers abreast of heinous new crimes, the names and faces of suspects, and the arrests that result from this "AMW" dragnet.

"I see the worst of society during the week," Walsh is fond of saying, "and then, on a Saturday night, I see the best of society: people doing the right thing, making the call."

Not playing vigilante, he emphasizes. Just sharing what they know.

"All the people who are with me on this show and this mission, we have changed the process of how law enforcement deals with missing children, missing adults, rape cases and serial killers," he declares.

Walsh and his wife Reve (who in 1984 co-founded the National Center for Missing & Exploited Children) have three kids, with the two youngest still at home. But the demands of "AMW" keep him on the move — shooting segments for the program, sharing tips with police, lobbying lawmakers, rallying his nationwide community watch.

On the air or in person, Walsh is a forceful presence. In recent years, his familiar face has grown craggier. His hair is gray and his voice more gravelly. But he is no less telegenic or strikingly credible. By some fortunate twist, he has always looked the part of someone doing exactly the kind of work he does. The image he brought with him to his role as an advocate underscores the truth of the advocate he became.

For him, the whys tied to crimes don't really matter — nor do the excuses.

"I don't buy it when the rapist says, 'I couldn't get a date 'cause I was fat and had acne.' Or the killer says, 'I did it 'cause I ate too many Twinkies.' There's lots and lots of people in this country who come from terrible, dysfunctional homes and didn't choose to hurt other people. They chose to function in society."