A federal grand jury has indicted Harold Thomas Martin III, the former NSA private contractor who prosecutors say spent decades stealing national security secrets, on charges that could see him serve a lengthy prison term if he's convicted.

When federal prosecutors charged Martin, a 52-year-old U.S. Navy reservist, with using his Top Secret security clearance to amass a huge cache of paper and electronic documents, the Justice Department called the case "breathtaking in its longevity and scale."

Martin has been in custody since a search of his home in suburban Maryland turned up "six bankers boxes' worth of paper documents and 50,000 gigabytes of electronic materials," as NPR's Carrie Johnson reported.

As Carrie notes, the charges of "willful retention of national defense information" that Martin now faces come from a section of the Espionage Act.

Martin worked at the Pentagon and the NSA for the contractor Booz Allen Hamilton. The government says that from December 1993 through Aug. 27, 2016 — the date of his arrest — Martin worked for at least seven different private companies and was assigned as a contractor to work at "a number of government agencies."

If he's convicted, Martin could face a maximum sentence of 10 years in prison for each of the 20 counts against him, according to the the U.S. Attorney's Office in Maryland. The defendant is slated to appear in federal court in Baltimore at 11 a.m. ET on Tuesday.

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