For the past 16 years, the Pentagon's top Cuba specialist, Ana Belen Montes, spied for Havana.
Now, Montes will tell U.S. officials the secrets she betrayed, including the unmasking of four U.S. agents working in Cuba.
Montes, 45, whose security clearance allowed her to brief senior officials, including the defense secretary, pleaded guilty Tuesday in federal court to an espionage charge.
Her case represents the most serious penetration of American intelligence ever by Cuba.
Montes, a U.S. citizen of Puerto Rican descent, didn't spy for money. She did it because she opposed U.S. policy toward Havana, U.S. officials and her lawyer say.
"She felt the Cubans were treated unfairly by the U.S. government," said her lawyer, Plato Cacheris, in an interview Wednesday.
Under a plea agreement, Montes will be sentenced to 25 years in prison Sept. 24, if she tells investigators everything. The charge, conspiracy to commit espionage, carries the death penalty.
Cacheris said "our bargaining chip" in negotiations with prosecutors was her spy tale. "The government gets the full story about what she did and how she did it," he said.
It should make for a provocative yarn.
Public documents already suggest a classic spy thriller, featuring encrypted transmissions and water soluble paper "to permit its rapid destruction in emergency."
But in her role as senior intelligence analyst at the Defense Intelligence Agency, which produces military intelligence about foreign countries, Montes was in a position to brief, and perhaps influence, top defense officials on Cuban issues.
The information Montes provided "could have an impact on policy," said Navy Lt. Cmdr. James E. Brooks, a DIA spokesman. "Did she mislead somebody?"
In 1998, Montes helped draft a report that the Cuban military no longer posed a threat to the United States.
Until DIA, CIA and FBI officers debrief Montes, Brooks said, officials will not know how much damage she did to national security.
The FBI, the lead agency in the investigation, said the interviews with Montes will be part of the government's damage assessment.
If she comes clean, the FBI said Wednesday, the plea agreement stands. If not, she could face a harsher penalty.
"What we get out of this," Brooks said, "we learn how she did it, who she talked to, what information she provided to the Cubans."
The Cuban government didn't pay Montes much, mainly travel expenses.
In a way, her motivation helped her get away with espionage for so long, Brooks said. "She was a very good spy in the fact that she didn't fit the typical stereotype of a spy," he said.
She wasn't greedy, Brooks said.
And she wasn't flashy.
Montes came under suspicion in December 2000. Brooks referred further questions about why it took so long to catch Montes to the FBI. He noted that the DIA administers polygraphs to employees.
The FBI declined to take the question, saying the case was still pending.
Van A. Harp, however, the assistant FBI director in charge of the Washington field office, characterized the Montes case as "a classic case of espionage and counterespionage."
People who know Montes say she didn't call attention to herself.
At Georgetown University's Caribbean Project, an informal study group of academics, policy analysts and activists with an interest in Cuba, she never voiced an opinion of U.S. policy.
Bill Leogrande, a professor of political science at American University, says he has been running into Montes for several years at area conferences. He is particularly familiar with her writings on Cuba.
"Everybody who covers Cuba here in Washington runs into each other," Leogrande said. "I would say she tended to be on the quiet side."
He added, "That's not unheard of for people from the intelligence community."
Montes was born on a U.S. military base in Germany. She grew up in the suburbs of Topeka, Kan., and Baltimore. In 1992, she was selected for the Exceptional Analyst Program and later traveled to Cuba to study the Cuban military.
Montes joined the DIA from the Justice Department in September 1985, prosecutors say. By the time she joined DIA, she was already working for the Cubans, officials say. Investigators want to know whether her Cuban handlers specifically asked her to try to join DIA.
Montes worked at Bolling Air Force Base in Washington as an intelligence research specialist, intelligence officer, and, at the time of her arrest last September, as a senior intelligence analyst. Montes had focused on Cuba since 1992.
The indictment against Montes says she refused promotions so she could keep spying for Havana.
A statement by the U.S. attorney for the District of Columbia says Montes compromised "secret" and "top secret" information "relating to the national defense as well as the identities of four covert United States intelligence officers."
Officials say the agents were not harmed.
"Montes communicated with the Cuban Intelligence Service through encrypted messages and received her instructions through shortwave encrypted transmissions from Cuba," the statement said.
"In addition, Montes communicated by coded numeric pager messages with the Cuban Intelligence Service by public telephones located in the District of Columbia and Maryland."
The codes included "I received message" or "danger." "All of this information," the statement said, "was on water soluble paper that could be rapidly destroyed."
Cacheris said the evidence against his client was overwhelming. Asked Wednesday how his client was doing, he said, "Under the circumstances, she's doing very well.
"Of course," he added, "she has some regrets. She'll express that at the time of her sentencing."
_ Information from the New York Times and Washington Post was used in this report.