Rep. Ileana Ros-Lehtinen, a Cuban-born south Florida Republican, said Castro should be charged with murder for the Cuban government's February 1996 shootdown of two planes belonging to the Cuban exile group Brothers to the Rescue.
Three Cuban-Americans and a Cuban exile died when Cuban government MiGs shot down two of the Brothers' small planes over international waters.
"Now that Fidel has formally stepped down as head of state, it clears the path for immediate legal action to be taken by the U.S. government," the Cuban-born Ros-Lehtinen, an outspoken critic of Cuba's government, said in a statement on Tuesday.
"This is but the first step in bringing Fidel and other Cuban war criminals to justice," said Ros-Lehtinen, who demanded Castro's indictment in an open letter to U.S. Attorney General Michael Mukasey.
The ailing, 81-year-old Castro announced on Tuesday he would not return as head of state, 49 years after he seized power in an armed revolution. He has not appeared in public since undergoing stomach surgery and handing power temporarily to his brother Raul Castro in July 2006.
Castro is an icon to leftists, and any U.S. indictment could be seen as an attempt to humiliate the bearded revolutionary who survived a CIA-backed invasion at the Bay of Pigs in 1961, as well as repeated assassination attempts.
But it would be applauded by many in Miami's politically powerful Cuban exile community, where Castro has long been reviled as a dictator and thug.
Ros-Lehtinen did not address the issue of how Castro could be brought before a U.S. court to answer charges.
A Justice Department spokesman said he was unaware of any plans to bring charges against Castro for the aircraft downings. The U.S. Attorney's Office for the Southern District of Florida did not immediately return calls seeking comment.
Although no charges could be filed without the approval of the Bush administration, whose term ends in January 2009, experts said Castro had relinquished any potential legal immunity by retiring as head of state.
Some other Latin American leaders have been legally targeted outside their countries after leaving office.
A Spanish judge tried in the late 1990s to extradite former Chilean dictator Augusto Pinochet from London on human rights charges. Spain's High Court has pursued a probe of former Guatemalan dictator Efrain Rios Montt on genocide charges, although Guatemala refuses to extradite him.
"It's a pretty strong case," Kendall Coffey, a former U.S. attorney for South Florida who has represented Cuban exiles in high-profile cases including the failed battle to keep Cuban-born Elian Gonzalez in the United States against the wishes of his father and Castro's government.
"It's undeniably a murder of three U.S. citizens and a lawful permanent (U.S.) resident over international airspace, over international waters, that was directed at the highest levels of the Cuban government," he said.
Jose Basulto piloted one of the Brothers to the Rescue planes that survived the 1996 shootdown. He said both Fidel Castro and his brother and designated successor, Raul, should face U.S. charges in the case.
"Both ... have been documented as accepting responsibility for the murders," Basulto told Reuters.
"I believe the United States should proceed now with the indictments," he added. "It's a matter of political will that's been missing so far."
(Additional reporting by Michael Christie in Miami and Jim Vicini in Washington, editing by Peter Cooney and Patricia Zengerle)
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