DETROIT (AP) — A Michigan man who admitted to exploiting a girl was sentenced Thursday to 30 years in federal prison in an investigation of a sinister online community that pressures children into committing acts of self-harm and Grayson  Prestoncreating sexual abuse images.

Richard Densmore ran chat rooms as a member of 764, an international group that targets kids online, particularly children with mental health challenges, the U.S. Justice Department said.

“This group seeks to do unspeakable harm to children to advance their goals of destroying civilized society, fomenting civil unrest and ultimately collapsing government institutions,” Assistant Attorney General Matt Olsen told reporters.

Densmore, 47, received the maximum sentence from U.S. District Judge Hala Jarbou during an appearance in federal court in Lansing.

“It is quite difficult, really, to overstate the depravity of Mr. Densmore’s crime and the threat that criminal networks like 764 present,” said Mark Totten, the U.S. attorney in western Michigan.

Densmore in July pleaded guilty to sexual exploitation of a child, acknowledging that he received a video of a nude girl with his nickname written on her chest. In a court filing, the government said that he had more victims and that his actions made him a “sensation” among allies.

Defense attorney Christopher Gibbons did not immediately return a message seeking comment after the sentencing. In a court filing, he said Densmore, an Army veteran, freely admitted his wrongdoing.

“He has not minimized the extent and wrongfulness of his conduct,” Gibbons wrote.

Assistant U.S. Attorney Adam Townshend said Densmore and others bragged about having images of children cutting and abusing themselves, “which they treated as trophies, social currency, and leverage to extort children into a cycle of continuous abuse.”