Ana Montes, accused of spying for Cuba, is freed after 20 years in prison.

(CNN) — Ana MontesA U.S. citizen accused of spying for Cuba has been released from a U.S. federal prison in Fort Worth, Texas, according to Federal Bureau of Prisons online records.

Cuba recruited Montes to spy in the 1980s and he was employed as an analyst in the Pentagon’s Defense Intelligence Agency (DIA) from 1985 to 2001. Eventually he was promoted to chief inspector of Cuba.

On September 21, 2001, Montes was arrested in Washington and charged with conspiracy to provide security information to Cuba.

In early 2002, he was sentenced to 25 years in prison after pleading guilty to espionage. The judge who sentenced Montez ordered him to be on five years of supervised release.

Upon Montez’s release, Florida Senator Marco Rubio criticized Montez for betraying the United States and aiding Cuba’s communist regime.

“Although Ana Belon Montes is in prison, Americans need to remember who she really is. If we forget the story of this spy, it will surely happen again,” Rubio said in a statement released this Saturday.

This is how they hired the Queen of Cuba

Now 65 years old known as Ana Montes Queen of CubaExperts say the U.S. does not know the full extent of the damage to Havana, which has transferred many U.S. military secrets to Havana for more than a year and a half.

In 1984, Montes clerked at the Washington Department of Justice and was pursuing a master’s degree at Johns Hopkins University.

He often criticized President Ronald Reagan’s support for rebels fighting pro-communist regimes in Central America.

“I felt that the United States had no right to impose the will of the United States on other countries,” said FBI Special Agent Pete Lapp, who led the investigation against Montes and eventually arrested him.

Her anger at American foreign policy complicated her relationships and attracted the attention of Cubans, who pushed her to withdraw from her friends, family and her own country.

Someone at Johns Hopkins noticed Montes’ passionate views on Cuba, and he was soon introduced to recruiters and agreed to help the Cuban cause.

At the same time, Montes applied for a job at the Defense Intelligence Agency, where workers deal with US military secrets on a daily basis. When he started there in 1985, the FBI says he was already a full-fledged Cuban spy.

How did she get caught?

One night in 1996, Montes was invited to give a briefing at the Pentagon during an international event, but he broke protocol by staying on duty until he was fired. This raised doubts.

Four years later, DIA counterintelligence agent Scott Carmichael hears that the FBI is looking for a mole: an unidentified spy at the DIA working for Cuba.

The suspect traveled to the U.S. naval base at Guantanamo Bay, Cuba at the time. When he searched the list of DIA employees who went to Guantanamo on those dates, a familiar name came up: Ana Montes.

“As soon as I saw his name, I knew it,” Carmichael said.

After that, Carmichael and FBI agent Laub team up to prove that Cuba’s DIA queen is actually a spy.

Through “high sensitivity” intelligence, it was revealed that an unidentified DIA mole purchased a specific computer and model at a specific time in 1996 from an unknown store in Alexandria, Virginia.

The lab was able to find the original store record linking that computer to Montes, confirming his beliefs.

CNN’s Thom Patterson contributed reporting.