Los Angeles (CNN) -- Federal authorities announced Tuesday they dismantled an international child pornography ring that allowed its 35 male members to trade thousands of images and videos of boys in sexually explicit situations through a website.

The announcement was made in the wake of Monday's guilty plea by a Georgia man to transporting child pornography using a secret Internet bulletin board called "Lost Boy." That website operated from September 2007 to January 2009, when authorities shut it down and began investigating the men who operated it, officials said.

"After a two-year investigation, we believe we have pursued all avenues, and our comments won't jeopardize the investigation," said Andre Birotte Jr., the U.S. attorney in Los Angeles, where authorities first discovered the existence of the global child porn ring.

"We felt this was the right time to come forward," Birotte added. "We are not talking about innocuous photographs.... I'm talking about serious graphic images of boys being sexually exploited."

David Michael Fagerness, 44, pleaded guilty Monday in U.S. District Court in Los Angeles to conspiracy to transport child pornography, officials said.

Fagerness, whom authorities said was from the Atlanta area, had relocated to the Czech Republic after being convicted of possessing child pornography in a Florida state court in 2005, but the Czech Republic ordered his return to the United States to face the federal charges, officials said.

Fagerness now faces a 15-year mandatory minimum sentence, and his sentencing is scheduled for June 6, 2011, prosecutors said.

Another alleged ring member, who was a registered sex offender, even used public library computers to access the Lost Boy website, but James Criscione, a 53-year-old Los Angeles attorney, died in custody earlier this year while facing charges, authorities said.

In all, 16 of the shuttered website's 35 male members have been charged in the United States for their roles in the ring, and five of them have entered guilty pleas, with two more expected to plead guilty later this month, authorities said. Eight of the defendants face federal charges of engaging in a child exploitation enterprise, which carries a mandatory 20-year sentence, officials said.

Four more defendants are named in an indictment but remain in Belgium, New Zealand, Germany and France, authorities said.

The remaining men in the child pornography ring are being sought, but in many cases, authorities have only their screen names and not their identities, officials said.

The investigation has also led to the identification of 27 victims of child abuse in the United States, including some whose images were posted on the Lost Boy bulletin board, officials said.

Authorities discovered the Lost Boy website after Eurojust, the judicial cooperation arm of the European Union, provided U.S. officials with leads from Norwegian and Italian authorities indicating that a man in North Hollywood, California, was communicating with an Italian national about child pornography and how to engage in child sex tourism in Romania, officials said.

Authorities found that the Lost Boy bulletin board had 35 adult male members, 15 of whom were U.S. nationals, officials said. Home countries of other members also included Brazil and Canada, officials said.

"Through unprecedented cooperation with foreign law enforcement partners, we have brought down a global online group whose principal purpose was to victimize children," said U.S. Assistant Attorney General Lanny Breuer.

The network had a vetting process for new members, most of whom had to post child pornography to join the organization, officials said.

Once accepted, members had to post child pornography to remain in good standing and not be removed from the board, officials said. Members traded techniques to evade detection by law enforcement, which included using screen names to mask identities, officials said.

The bulletin board also had a "Handbook Project," where members contributed to a guide on how to find and groom boys to engage in sex and how to move on to other victims when the current victim grows too old to be attractive to the members, authorities said.