MIAMI (AP) — Federal prosecutors are seeking to revoke the U.S. citizenship of former U.S. Ambassador Manuel Rocha, the imprisoned former diplomat who served as a secret agent for Cuba dating back to the 1970s in one of the longest-running betrayals in the history of the foreign service.

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The U.S. Attorney's Office in Miami filed a civil denaturalization complaint Thursday that would complete the Colombian-born Rocha's fall from grace, stripping him of the citizenship he attained after moving to New York City at age 10 with his widowed mother and two siblings.

Rocha, 75, was arrested in late 2023 and later sentenced to 15 years in federal prison after admitting he worked for decades as a secret agent for communist Cuba. He was secretly recorded by an undercover FBI agent praising Fidel Castro as "El Comandante" and bragging about his work for Cuba's communist government, calling it "more than a grand slam" against the U.S. "enemy."

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The plea to 15 federal counts averted a trial that would have shed new light on what, exactly, Rocha did to help Cuba even as he held prestigious State Department postings such as ambassador to Bolivia and top posts in Argentina, Mexico, the White House and the U.S. It's not even clear when federal prosecutors first suspected Rocha was spying for Cuba.

As part of his plea agreement, Rocha acknowledged that he first connected with Cuban intelligence agents in 1973 — five years before applying for U.S. citizenship — while attending a student program in Chile at the end of socialist President Salvador Allende's rule. Shortly after, at the direction of Havana, he enrolled in master's programs at Harvard and Georgetown Universities on his way to getting hired by the U.S. State Department.

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The government generally faces a high burden of proof in revoking citizenship, as federal law requires prosecutors to show convincing evidence that an individual attained citizenship illegally or procured naturalization by "concealment of a material fact or by willful misrepresentation."

Prosecutors alleged in court filings that Rocha lied under oath that he "believed in the U.S. Constitution" and had no affiliation with the Communist Party of Cuba while applying for citizenship in 1978.

"The Southern District of Florida helped take down one of the most prolific Cuban spies ever uncovered in the United States," said U.S. Attorney Jason A. Reding Quiñones for the Southern District of Florida. "This civil denaturalization case is about finishing the job."

The Justice Department has significantly increased its focus on denaturalization cases in recent years, and last year issued an internal memo to prosecutors directing them to prioritize cases against people who "pose a potential danger to national security," including those involving terrorism and espionage.

The Trump administration moved this week to denaturalize 11 other people accused of crimes, including child sexual abuse and providing material support to terrorists. The denaturalization process was used in only about a dozen cases per year between 1990 and 2017.

An Associated Press investigation into Rocha found several red flags overlooked along the way, including a warning that one longtime CIA operative received nearly two decades ago that Rocha was working as a double agent. Separate intelligence revealed the CIA had been aware as early as 1987 that Cuban leader Fidel Castro had a "super mole" burrowed deep inside the U.S. government, and some officials suspected it could have been Rocha.

Over the past two years, the FBI, U.S. State Department and CIA have been working to decipher the case's biggest missing piece: exactly what the longtime diplomat may have given up to Cuba. Rocha spent the first several months of his imprisonment being debriefed by federal officials, but it's not clear what new information was gleaned from those sessions.