A St. Tammany Parish man who ran a massive child pornography ring that duped young boys into creating sexually explicit footage of themselves was sentenced Thursday to 21 years in federal prison.

Jonathan S. Johnson, 28, who lived outside Abita Springs, faced a possible life sentence but was credited for helping law enforcement officials build cases against several co-defendants in what the authorities called a “child exploitation enterprise.” He pleaded guilty last year.

Johnson, who has been in custody since June 2013, administered a sophisticated network that collected thousands of illicit videos, many of them featuring prepubescent boys. It had grown to include more than 27,000 members from around the world.

Users of the underground websites had access not only to a library of child pornography but also to tutorials that explained how to create fake female personas online in order to entice — and then film — unsuspecting young boys using Web cameras. Members of the sites were required to register with a username and password, which allowed them to download files, exchange private messages and comment on videos, prosecutors said.

Clad in a red prison jumpsuit, Johnson told U.S. District Judge Nannette Jolivette Brown on Thursday that he would do things differently if he had the chance. He said he had been at a low point in his life when he began the child porn operation.

Johnson’s mother also addressed the judge briefly, insisting her son had been a “good kid.”

“He’s an adult now,” Brown responded.

Johnson’s mother found herself locked outside the courtroom as Brown read impact statements from victims, a portion of the hearing held under seal.

She said she had been surprised at the allegations against her son.

“Computers are destroying a lot of kids’ lives,” she said.

Johnson’s operation was described in court filings as a “hidden service board” that existed in an anonymous corner of the Internet. Users would mask their data transfers and locations through “the onion router,” a popular software known as Tor that enables anonymous Web browsing.

Authorities have said the scope of the case against Johnson and his co-defendants was unprecedented. Homeland Security Secretary Jeh Johnson said last year that it marked one of the largest online child exploitation investigations that U.S. Immigration and Customs Enforcement has ever seen.

Raymond R. Parmer Jr., the special agent in charge of Homeland Security investigations in New Orleans, said in a statement that “there is simply no room in our society for such monsters.”

“As the ringleader of a pack of sadistic child predators,” Parmer said, Johnson “is responsible for the sexual exploitation of hundreds of young victims, whose documented abuse was subsequently distributed to thousands of perverted criminals.”

The case, which became known as “Operation Roundtable,” led to charges in New Orleans federal court against 10 other people— all of whom have pleaded guilty — and prompted related investigations around the country and overseas into potential subscribers.

The authorities identified at least 250 victims in 39 states and five foreign countries.

More than two dozen other defendants were charged around the United States and Canada, said Anna Christman, a spokeswoman for U.S. Attorney Kenneth Polite Jr.

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