A former National Security Agency contractor on Thursday pleaded guilty to stealing secret defense information over two decades in what legal experts have described as the biggest breach of classified information in U.S. history.
In his plea deal in U.S. District Court in Baltimore, Harold Thomas Martin III admitted to removing highly classified digital and hard copy documents, then storing them in his home and car from the late 1990s through 2016.
Prosecutors say there is no indication Martin ever shared the stolen secrets. His defense attorneys say he simply hoarded the information.
Martin, who held multiple security clearances while working at government agencies as a private contractor, said he knew stealing the documents risked the country's security.
He pleaded guilty on Thursday to one felony count of willful retention of national defense information. He could be sentenced to nine years in prison.
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The FBI arrested Martin, now 54, in August 2016 at his home in Glen Burnie, Maryland. A former U.S. Navy lieutenant, Martin has been in federal custody since then.
Martin initially pleaded not guilty to 20 counts of willfully retaining classified information and was due to go to trial in June, but prosecutors announced he would be arraigned again this week.
Federal defenders said he did not intend to harm the country or intelligence agencies. On Thursday Martin told a federal judge he was diagnosed with ADHD.
"His actions were the product of mental illness," his federal defenders’ statement said. "Not treason."
One of his lawyers previously described Martin as a “compulsive hoarder” who took home work documents.
The misuse of classified information follows several other NSA breaches, including when Eric Snowden exposed government surveillance programs in 2013. Last September, another a former NSA computer developer was sentenced to five and a half years in prison for storing troves of sensitive documents at his home.
Steven Aftergood, a government secrecy specialist with the Federation of American Scientists, said the breaches have intensified with modern technology.
“The string of breaches is a humbling reminder that keeping secrets is hard, that people are fallible, and that perfect security can never be achieved," Aftergood said in an email. "What has changed over the past several decades or so is that the scale of the breaches has increased tremendously. Instead of individual secrets being compromised, it often turns out that entire databases or libraries of information.”
Contributing: The Associated Press
This article originally appeared on USA TODAY: Ex-NSA contractor pleads guilty to hoarding national defense information in massive breach