A group founded by Cuban exiles known as Brothers to the Rescue is at the center of the U.S. Justice Department's decision to seek an indictment against Cuban leader Raúl Castro, a move that would revive one of the lowest points in the two countries' bitter decadeslong relationship.

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Before the indictment was announced Wednesday, a person familiar with the investigation told The Associated Press that it was connected to Castro's alleged role in the 1996 shootdown of two planes operated by the Miami-based exile group. Castro was defense minister at the time, making him the nation's highest authority after his brother Fidel.

The person spoke on the condition of anonymity because they weren't authorized to discuss an ongoing investigation.

What is Brothers to the Rescue?

Brothers to the Rescue began operating in 1980 during 125,000 Cubans' unexpected emigration to the United States. Founded by emigré José Basulto, it aimed to help Cuban refugees in the Florida straits by dropping supplies from small planes and alerting the U.S. Coast Guard.

The monthslong crisis began after some Cubans protested travel restrictions imposed by President Fidel Castro's communist government and Castro opened the port of Mariel to anyone who wanted to leave, filling the Florida straits with desperate people.

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President Bill Clinton's administration changed immigration rules to discourage Cubans from heading north on rickety, makeshift boats. Meanwhile, Brothers to the Rescue, which is also known by its Spanish name Hermanos al Rescate, continued flying toward Cuban airspace and provoking Havana.

What happened with the planes?

On Feb. 24, 1996, three planes carrying members of Brothers to the Rescue entered a zone close to the 24th parallel, a short distance north of Havana and some of Cuba's highest-value targets.

Cuban fighter planes shot down two of the exiles' unarmed civilian Cessnas, killing all four men aboard. A third plane, carrying the organization's leader, narrowly escaped.

What did Cuba and the United States do to avoid the crisis?

American University Cuba specialist William LeoGrande and National Security Archive senior analyst Peter Kornbluh said this week that their 2015 book, "Back Channel to Cuba: The Hidden History of Negotiations between Washington and Havana," shows how the Clinton administration's repeated warnings about provoking Cuba did not stop Hermanos al Rescate.

"Only after the shootdown did the FAA issue a concrete 'cease and desist' order against Basulto for what it called 'careless or reckless' operations that 'endanger the lives or property of others,'" the pair wrote.

Between Hermanos al Rescate provoking the Cuban government, the U.S. failing to stop the group and the Cuban air force firing on civilian planes, "there's no good guys in this story," LeoGrande said.

Was anyone charged?

U.S. counterintelligence caught five Cuban intelligence agents who had infiltrated Brothers to the Rescue. The story was fictionalized in the movie "The Wasp Network."

Two of the Cuban agents served long sentences and three were released from custody in a prisoner exchange that came before former President Barack Obama's detente with Raúl Castro.

Two Cuban fighter jet pilots and their commanding officer who also were indicted in the shootdown have remained outside the reach of U.S. law enforcement while living in Cuba.

Associated Press reporters Eric Tucker and Alanna Durkin Richer in Washington, D.C. contributed.