For 16 years, Ana Belen Montes spied for Cuba from increasingly responsible positions at the Defense Intelligence Agency. If Havana has ever run a higher level or more valuable mole inside the American defense establishment, that has never been revealed.

When she was arrested in late September 2001, Montes was about the equivalent in rank of a colonel. She had access to sensitive compartmented intelligence. Strangely, for one so openly enamored of Fidel Castro, her superiors considered her one of the best Cuba analysts anywhere in government.

Despite the importance of her case, some of the most tantalizing questions about her spying have never been publicly answered. Could the calamity of her treason have been avoided? What was learned about Cuban intelligence tradecraft? How was she discovered? And, of enduring concern, did she work with other American spies thus far undetected or not prosecuted?

Thanks to researcher Jeffrey Richelson and the National Security Archive, new light has finally been shed on the Montes case. Because of their efforts, a 180 page study completed by the Department of Defense Inspector General in 2005 has recently been declassified. It is heavily redacted; many pages, including the CIA’s extensive comments, blacked out. Yet, a quantity of surprising new details are now on the public record.

Montes’s decision to spy for Cuba was “coolly deliberate.” Enticed by a Cuban access agent in Washington, they traveled together to New York in December 1984. Montes met with intelligence officers posted under cover at the Cuban mission to the United Nations.

She “unhesitatingly agreed” to work with them and travel clandestinely to Cuba as soon as possible. The following March, she went there via Spain and Czechoslovakia. The Pentagon report does not state the obvious: while there, she must have received specialized training in intelligence tradecraft.

Then, with Cuban encouragement, she applied for a job at DIA. A standard background investigation was conducted, but we now know that serious concerns about her suitability were raised. Without elaboration, the Pentagon report indicates that they included “falsification of her Master of Arts degree from Johns Hopkins (University) and her trustworthiness.”

DIA did not require applicants to submit to a pre-employment polygraph exam. So, Montes, a trained Cuban espionage agent with a problematic past was cleared and hired. She began her double duties in September 1985.

After her arrest, Montes insisted that she had the “moral right” to provide information to Cuba. In her view, she did not work for Cuba, but with Cuban officials. They felt “mutual respect and understanding” she thought, as “comrades in the struggle.”

The Cubans were skilled in manipulating and controlling her. She told interrogators after her apprehension that she considered herself the equal of her “Cuban comrades, not a menial espionage tool.” They let her believe she “maintained significant control,” although she consistently left “security matters, including meeting site security, countersurveillance, and transmission security” to her handlers.

Montes said they were “thoughtful, sensitive to her needs, very good to me.” They went to “special lengths to assure her they had complete confidence in her.” They allowed her a long, loose leash, easier because they were not paying for her extraordinary services.

Initially in New York, and later at her request in the Washington area, she met with her handlers as often as once every two or three weeks, usually on weekends. Everything about her second covert trip to Cuba is redacted in the Pentagon report.

In 1991, Montes underwent a seemingly routine security reinvestigation. She was asked about foreign travel, and lied. Questioned about inaccuracies in her original application for employment, she confessed that she had misrepresented an incident in her past. Feigning innocence, Montes claimed that she “did not understand the seriousness of being truthful and honest at the time.”

Her questionable case was then reviewed at a higher level. The adjudicator reported that “while Montes seemed to have a tendency ‘to twist the truth’ to her own needs and her honesty was still a cause of concern, adverse security action was unlikely.” Again, she had slipped through. Her high level clearances were recertified.

Soon after, she brazenly submitted a freedom of information request for her own government records. She must have been concerned that something adverse had been discovered. Investigative material was released. She gave the surprised Cubans copies.

She apparently visited Cuba a third time after being selected to participate in the prestigious Director of Central Intelligence “Exceptional Analyst Program” in 1992. This time her travel to the island, purportedly to conduct research, was legal.

In 1996, she was questioned by a DIA special agent after another DIA employee reported concerns about her. Serious doubts were raised about her veracity, but the allegations could not be substantiated.

None of this seems to have contributed to her eventual unmasking. So, how was she discovered? Surprisingly, revealing information seeps through the Pentagon’s report. “We got lucky,” a counterintelligence official observed. An entirely blacked-out section entitled “Serendipity” suggests the same.

By April 1998, a coordinated search for a Cuban spy was underway, according to the report. At first it was thought most likely the quarry was a CIA employee. Investigators were following a crucial clue: the unknown spy had apparently traveled to the Guantanamo naval base as Montes had apparently done on official DIA business.

The breakthrough had seemingly come earlier, however. According to the Pentagon report, Montes was informed shortly after her arrest that investigators “had information from a senior official in the Cuban intelligence service concerning a Cuban penetration agent that implicated Montes.” It appears that this information propelled the investigation that resulted in her arrest.

Who was this mysterious, previously unacknowledged source? From the language of the Pentagon report, it was probably not a defector, but more likely a renegade or compromised Cuban intelligence officer. If so, Montes was done in by one of her own so-called “comrades.”

Did she work with other American spies? The report is ambiguous; it states that after the terrorist attacks on September 11, 2001 pressure intensified to arrest Montes. The FBI preferred to wait, however, in order “to monitor Montes’s activities with the prospect that she may have eventually led the FBI to others in the Cuban spy network.”

Did government censors inadvertently confirm the existence of a larger spy ring? If in fact there was evidence of one, it may be a long time before more is known.

It is now clear, however, that Montes’s apprehension was not just the result of excellent intelligence work. She told investigators after her arrest that a week earlier she had learned that she was under surveillance. She could have decided then to flee to Cuba, and probably would have made it there safely.

But she said that “she couldn’t give up on the people (she) was helping.” Montes is serving a 25 year prison sentence.