A US federal judge has dismissed immigration charges against Cuban exile Luis Posada Carriles, a man convicted of blowing up a Cuban airliner in 1976.
Venezuela and Cuba want to put Mr Posada on trial
The judge accused the US government of "fraud, deceit, and trickery" in its handling of the case.
Posada, 79, was detained in May 2005 after entering the US illegally.
A former CIA employee, he is wanted in Venezuela and Cuba over the downing of a Cuban airliner in 1976 in which 73 people died. He denies involvement.
The judge's surprise decision leaves Posada's fate in doubt, though US authorities have ruled out returning him to Cuba or Venezuela.
"I am free," Posada exclaimed on a Miami-based radio station after the ruling, according to the AFP news agency.
"Thank God, you, all of my brothers, the people in Cuba... for this victory," he said.
Cuba reacted with anger at news that he had been cleared on Tuesday.
"This decision is an outrage to the Cuban people and to the nations that lost 73 of their sons and daughters in the heinous 1976 attack that blew up a civilian Cubana de Aviación aircraft off the coast of Barbados," a government statement said.
Havana accused the US of applying double standards in its war on terror because Posada was once employed by the CIA.
"The terrorist's release has been concocted by the White House as compensation for Posada Carriles not to reveal what he knows, not to talk about the countless secrets he keeps on his protracted period as an agent of the US special services," the statement said.
Venezuelan leaders have also accused the US of treating Posada with kid gloves because of his CIA past.
Posada was released on bail last month, but had been due to go on trial next Monday.
However, US district judge Kathleen Cardone dismissed the immigration fraud indictment in a court in El Paso, Texas.
Posada's lawyer, Felipe Millan, said his client had been "tricked" by the government.
Judge Cardone agreed.
"In addition to engaging in fraud, deceit and trickery, this court finds the government's tactics in this case are so grossly shocking and so outrageous as to violate the universal sense of justice," she wrote in her ruling.
"As a result, this court is left with no choice but to dismiss the indictment."
She accused officials of manipulating the evidence against Posada, namely by not telling him that what he thought was an immigration interview was actually a criminal interrogation. Speaking after the ruling, US justice department spokesman Dean Boyd said: "We're reviewing the decision."
A veteran anti-communist, Posada was jailed in Venezuela over the airliner bombing, but escaped from jail in 1985 during an appeal against his conviction.
He was then jailed in Panama in 2000 for plotting the assassination of his arch-enemy Cuban leader Fidel Castro, but was pardoned and released four years later.
US authorities are also reported to be investigating whether Posada was involved in the bombing of a Havana hotel, in 1997, that killed an Italian tourist.