Timothy DeFoggi, a former acting director of cybersecurity for the U.S. Department of Health and Human Services (HHS), was sentenced to 25 years in prison on Monday for disseminating child pornography. DeFoggi was convicted of the charges in August 2014.

The cybersecurity expert chatted with users of an underground online forum about his desire to rape and murder children. DeFoggi used the Tor browser, a service that could prevent authorities from tracking his activity, while working as HHS’s head of cybersecurity in 2013. He was still listed as an employee with top clearance following his arrest until January 2014.

“Using the same technological expertise he employed as acting director of cybersecurity at HHS, DeFoggi attempted to sexually exploit children and traffic in child pornography through an anonymous computer network of child predators,” Assistant Attorney General Leslie Caldwell said in a statement.

DeFoggi began trading graphic sexual images of children on the website in March 2012, which could not be found through traditional search engines or Web browsers, the Department of Justice said. The FBI shut down the site in December 2012.

“Dangerous criminals cannot be allowed to operate online with impunity,” Caldwell said. “Today’s sentence shows that the Department of Justice will bring criminals and child predators to justice, even when they employ anonymous networks like Tor.”

Five other users of the same child pornography website have been convicted so far, receiving 12 or more years in prison each, as Federal law enforcement cracks down on websites using the Tor network to hide criminal activities. In November, hundreds of hidden sites went down following an internationally coordinated police operation. In December, the DOJ announced a unit dedicated to cybersecurity within its Computer Crime and Intellectual Property Section (CCIPS).

“Those who think they are acting anonymously on the Internet will be found and held accountable,” said U.S. Attorney Deborah Gilg of the District of Nebraska, who prosecuted DeFoggi, said in the statement.