TAMPA, Fla. (AP) — A former U.S. Air Force intelligence officer was sentenced Thursday to three years in federal prison for keeping classified documents at his home and other unauthorized locations.

Robert Birchum, 55, was sentenced in Tampa federal court, according to court records. He pleaded guilty in February to unlawfully possessing and retaining classified documents relating to the national defense of the United States. Birchum was also fined $25,000.

According to the plea agreement, Birchum, who retired in 2018 as a lieutenant colonel, served in various positions in intelligence over his 29-year career, including those requiring him to work with classified intelligence information for the Joint Special Operations Command, the Special Operations Command and the Office of the Director of National Intelligence.

In 2017, law enforcement officers discovered that Birchum knowingly removed more than 300 classified files or documents, including more than 30 items marked top secret, from authorized locations, prosecutors said. Birchum kept these classified materials in his home, his overseas officer’s quarters and a storage pod in his driveway.

Prosecutors specifically noted that Birchum possessed two documents on a thumb drive found in his home that contained information relating to the National Security Agency’s capabilities and methods of collection and targets’ vulnerabilities. Their unauthorized release could have caused exceptionally grave damage to the national security of the United States, officials said.

There was no indication from investigators that Birchum ever distributed the classified material.