Kenneth Nighbert lived a block from the beach in Kennebunk, Maine. Two weeks ago, the retired Air Force pilot flew his American flag upside down from his second-floor sun deck, a universal cry for help. Then he went inside, tied a plastic bag around his head and died.

Nighbert, 49, was at the end of a long losing streak. He believed he had been unfairly passed over for promotion to lieutenant colonel. A business he started went bust, forcing him to take a $9-an-hour factory job. Then his wife left him, police said, taking along their teen-age daughter.

But the event that likely compelled Nighbert to put his affairs in order, get his uniform ready for burial, then asphyxiate himself on his bedroom couch took place Sept. 3, when he was snared in a 14-nation raid on an Internet pornography ring made up of people who allegedly were producing, selling, trading and, in Nighbert’s case, downloading pictures of little kids having sex.

Nighbert is notable not just because U.S. Customs Service agents had filed suit to seize possession of his home — a weapon they say they will increasingly deploy against Internet-cruising pedophiles — or because he allegedly was a member of a multinational “club” of men who swapped child pornography and commiserated inside a secret, exclusive chat room known as Wonderland. Or that he was swept up last month in the biggest Internet porn sting in history.

What makes his case unusual is the fact that his death was not: Nighbert is the fourth person to commit suicide of the 34 Americans either charged or somehow suspected in the case. Authorities say such deaths have become common, and in most instances the suicide victims are seemingly upstanding people who otherwise might not have been arrested if not for the deceptively anonymous lure of the Internet .

“They realize `Oh God, I’m caught.’ They end it,” said Special Agent Eugene Weinschenk, head of the Customs Service’s cybersmuggling center. He said a dozen accused pedophiles killed themselves during a big Internet porn sweep two years ago in Belgium and France. “We suspect it will not be the last,” he said of the Wonderland suicides.

Weinschenk said the crackdown on the Wonderland Club has generated enough leads for another, perhaps even bigger, series of raids of rings that swap child pornography “like baseball cards.”

And authorities expect to find more people like Nighbert, or the microbiologist at the University of Connecticut who slashed his wrists a few weeks ago, or the computer consultant in Colorado who shot himself in the head about the same time: People who think they’re indulging in forbidden fantasies in the solitude of their homes, only to be interrupted by a firm knock on their doors in the dead of night.

These people, experts say, are most likely to find suicide the only escape — not only from a possible prison sentence, but from humiliation and social censure on a scale beyond comprehension.

Michael Bailey, a Northwestern University psychologist who testified last year on behalf of a child molester who sought, and won, a court-approved castration, said no studies have been done on the propensity of pedophiles to kill themselves once they are found out. But the motivation is there.

“In general, people who suffer the humiliation of arrest are clearly at risk for suicide,” he said. “Think about how much worse it would be to get arrested for having sexual pictures of children.”

The Wonderland Club case is an offshoot of a 1996 investigation into the San Jose, Calif.-based Orchid Club and the subsequent arrest of men who sexually abused an 11-year-old girl and transmitted Internet photos of the assault.

Evidence in that case eventually led to a computer programmer in England and the much larger Wonderland Club, to which prospective members were required to supply 10,000 images of child pornography to join, Weinschenk said.

Using wiretaps, a seized list of user names and search warrants, the Customs Service, police in 22 states and authorities in 13 other countries carried out raids that resulted in roughly 60 arrests worldwide.

So far, 14 people have been charged in the United States, and Weinschenk said five are actually accused of sexually abusing children. He said perhaps a dozen of the thousands of children who turned up in the photos have been identified; in most cases they were relatives or neighbors of the accused.

The suspects range from a high school teacher to a 15-year-old boy to a quadriplegic man. Three women also were caught in the sweep.

On Monday, 31-year-old William J. Rosa, a former University of North Carolina-Chapel Hill medical student, became the first suspect in the Wonderland case to plead guilty to trading child pornography, though there was no evidence he molested anyone. His sentencing is in February.