“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.