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WASHINGTON—A former National Security Agency contractor amassed at least 500 million pages of government records, including top-secret information about military operations, by stealing documents bit by bit over two decades, the Justice Department alleged in a court filing submitted Thursday.

Prosecutors in August arrested and charged Harold "Hal" Martin III, of Glen Burnie, Md., with theft of government property and unauthorized removal or retention of classified documents. The case was kept under seal until earlier this month, when some details became public.

The new filing said the Justice Department would likely charge Mr. Martin with additional crimes, including violating the Espionage Act, an offense that carries much stiffer penalties than the current charges.

Mr. Martin's attorney, Jim Wyda, declined to comment on the new filing. In the past, he has said that Mr. Martin is a patriotic American who has served his country.

A federal court has scheduled a hearing for Friday to consider whether Mr. Martin should be released while awaiting trial. The Justice Department released its 12-page document ahead of that hearing, detailing new allegations about the scope of Mr. Martin's alleged theft and suggesting he had become heavily armed, accumulating 10 weapons, and had taken sophisticated steps to cover his tracks.

Some former associates had described Mr. Martin as a harmless hoarder who suffered from post-traumatic stress disorder. The new government filing paints a different picture, raising questions about his motives and suggesting he was capable of sharing U.S. secrets with the nation's adversaries and potentially putting American lives at risk.

The document doesn't, however, answer one of the big questions in the case: whether Mr. Martin shared any of the stolen classified information with another person or another country. The document offers no evidence that he did but suggested Mr. Martin had the capacity to do so.

Mr. Martin, a former Naval officer, was most recently a contractor at Booz Allen Hamilton Holding Corp., a job that placed him inside some of the government's most secretive programs inside the NSA and the Pentagon. The Justice Department said that a search of his home and his automobile uncovered "thousands of pages of documents and dozens of computers and other storage devices and media containing, conservatively, fifty terabytes of information."

Fifty terabytes is equivalent to 50,000 gigabytes. One gigabyte can contain 10,000 pages of documents, the department estimated.

By extrapolation, 50 terabytes can hold 500 million pages.

In seeking Friday's hearing, Mr. Martin's legal team wrote that he "is neither a flight risk nor a danger to the community, and to the extent either of these factors is a concern, they can be sufficiently addressed with specific release conditions."

The Justice Department countered Thursday that Mr. Martin "presents a high risk of flight, a risk to the nation, and to the physical safety of others."

Mr. Martin worked on highly sensitive programs, people familiar with the investigation have said, including those involving an arsenal of cybertools the government has amassed to use against other countries as well as cyberweapons that were in development.

So far, it is unknown what Mr. Martin intended and what, if any, plans he had for the pilfered information.

When the Federal Bureau of Investigation searched Mr. Martin's home and car in August, it found much of the stolen information in plain sight. Top-secret information was stored in his car, which wasn't parked in a garage. Investigators also found an email chain printed out in that car that was marked "top secret" and contained "highly sensitive information."

They also found handwritten notes that appeared to describe the NSA's classified computer infrastructure, the Justice Department said in its filing.

"Among the many other classified documents found in the Defendant's possession was a document marked as 'Top Secret/Sensitive Compartmented Information' ('TS/SCI') regarding specific operational plans against a known enemy of the United States and its allies," the court document said.

Government lawyers argued that releasing Mr. Martin would present an obvious danger.

"As a result of the extensive publicity this case has received, it is readily apparent to every foreign counterintelligence professional and nongovernmental actor that the Defendant has access to highly classified information, whether in his head, in still-hidden physical locations, or stored in cyberspace—and he has demonstrated absolutely no interest in protecting it," the Justice Department said. "This makes the Defendant a prime target, and his release would seriously endanger the safety of the country and potentially even the Defendant himself."

The filing described Mr. Martin as computer genius who easily outsmarted government efforts to protect secrets and said he possessed an advanced understanding of how to encrypt messages and hide information in cyberspace.

In July 2016, according to the document, Mr. Martin went to Connecticut and bought a "detective special" police-package Chevrolet Caprice. The FBI found 10 firearms in his possession, including an AR-style tactical rifle and a shotgun with a flash suppressor.

Scott Calvert contributed to this article.

Write to Damian Paletta at damian.paletta@wsj.com

(END) Dow Jones Newswires

October 20, 2016 17:55 ET (21:55 GMT)

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