“He was one of the most patriotic people I knew,” Ms. Martin said in a telephone interview. More likely, she said, he got in the habit of taking material home to keep working at night.
“He brought work home all the time — he was always on a laptop, always working, always studying,” she said, adding that he had piles of books and papers everywhere and was “a bit of a hoarder.” She called him “a genuinely nice guy — a little eccentric, but not in a bad way.” He had no interest in politics, she said, and was interested mainly in computers.
Among the leaks that officials believe did not come from Mr. Snowden, a former N.S.A. contractor like Mr. Martin, are two of particular concern. They involve techniques used by the agency to break into foreign computer systems and networks — sometimes even computers not connected to the internet. Others, published by WikiLeaks, included lists of eavesdropping targets and transcripts of intercepted communications from American allies.
So far, F.B.I. agents and intelligence officials, too, are skeptical that Mr. Martin was the source for them. They are pressing Mr. Martin to explain everything he did with the classified material, appealing to his patriotism, said a law enforcement official who would speak about the continuing investigation only on the condition of anonymity. And they have told Mr. Martin that if he does not say what he did with the information, the N.S.A. may be forced to shut down vital national security programs that could have been compromised, the official said.
Mr. Martin was arrested at his home in Glen Burnie, Md., south of Baltimore, shortly after the F.B.I. first learned that he might have taken home classified material. He had worked since 2009 for an N.S.A. contractor, Booz Allen Hamilton, and was transferred away from the N.S.A. last year.
At the time of his arrest, Mr. Martin was working as a Booz Allen contractor in Alexandria, Va., for the Pentagon’s Office of Acquisition, Technology and Logistics, according to two people briefed on the investigation.
Even if he was not behind the leaks, Mr. Martin may face up to 11 years in prison for taking classified material without authorization and keeping it in an insecure setting.
Post-Snowden Leaks of N.S.A. Secrets
Here are some major leaks of classified information that appear not to have come from Edward J. Snowden:
“Let’s just say he’s only a psycho hoarder and he keeps this stuff with his old copies of National Geographic and his collection of lunchboxes,” said an administration official, who also asked not to be named. “That’s still extremely troubling to anyone in national security, because people like that don’t keep track of where things are or with whom they are talking.”
In Mr. Martin’s case, the official said, the sloppy handling “is particularly worrisome — we are talking sources and methods, tactics, techniques and procedures. Those are the things we guard most closely.”
Rajesh De, who was general counsel to the N.S.A. and is now the chairman of the cybersecurity practice at the law firm Mayer Brown, said it was “risky making the investigative leap from the fact that some individual has taken information to the conclusion that they have revealed it.” Often, the information that one insider has is also available to others.
Investigators have found that over the years, Mr. Martin’s methods changed with the times — at first, he took documents on paper, later on CDs and more recently on thumb drives. They are comparing the documents he took with those that have appeared on WikiLeaks and other sites.
They are exploring the possibility, however remote, that someone might have hacked into his home computers, which had minimal security protections. And they are continuing to look for other ways the secrets may have escaped, from another insider or from sophisticated hackers.
Meanwhile, a more nuanced portrait of Mr. Martin is emerging from his ex-wife and others who know him, some of whom spoke on the condition of anonymity.
His Navy record shows that he enlisted in 1987, was commissioned as an officer the next year, served in Operation Desert Storm in Iraq, joined the Navy Reserve and eventually left the reserve in 2000.
Roy Rada, a retired professor at the University of Maryland, Baltimore County, who mentored Mr. Martin during his early Ph.D. research, said he had been very interested in post-traumatic stress disorder and how to diagnose it quickly using eye-tracking. By Mr. Rada’s recollection, Mr. Martin believed that he had many of the symptoms of PTSD, possibly a result of his service in Desert Storm.
Mr. Martin sought funding from military health agencies to carry out a major research project on PTSD diagnosis, Mr. Rada said, but his proposals were not funded.
Mr. Rada said he had found Mr. Martin “thoughtful, sensitive and dedicated.” But he said his former student sometimes seemed to feel that he and his work were “inadequately appreciated,” possibly because he was on a campus of students and professors with little knowledge of the military.
Another person who knew him well years ago, and did not want to be quoted by name talking about his shortcomings, said that Mr. Martin had a sort of “Walter Mitty complex” that occasionally led him to dream of being more important than he was or to embellish his achievements.
Once, the person remembered, he decided to buy an unmarked police car, and he traveled to Georgia to pick up the car, which had a spotlight installed in the side and other special equipment.
“He just always wanted to be important,” she said.