Douglas Martin / New York Times News Service

Orlando Bosch, a Cuban-American pediatrician and militant Cuban-exile leader who was accused, and then acquitted, of masterminding the 1976 bombing of a Cuban airliner in which 73 people were killed, died Wednesday in Miami. He was 84.

His family announced the death. He had been hospitalized with a number of illnesses.

Bosch became a lightning rod in the Cuban-exile world. His supporters called him a hero, holding rallies for him and lobbying to name a Miami expressway after him. Richard Thornburgh, when he was the U.S. attorney general under President George H.W. Bush, called him “an unreformed terrorist.”

Bosch maintained that he had fought a “just war” against Fidel Castro — calling him “a monster” — often with support by the American government.

In the airliner bombing, the plane had left Barbados for Jamaica and exploded over the Caribbean, killing all 73 aboard. Four people were arrested, three of them Venezuelan residents.

Tried in Venezuelan courts, two of the defendants were convicted and sentenced to 20 years in prison. But Bosch, who along with another exile leader, Luis Posada Carriles, was charged with masterminding the plot, was acquitted after much of the prosecution’s evidence was ruled inadmissible. Posada, who had sometimes worked for the Central Intelligence Agency, escaped to Panama before he was tried.

In a CIA report that was later declassified, Posada was said to have been overheard saying, “We are going to hit a Cuban airplane” and “Orlando has the details.” And in 2006, the FBI released a report quoting an informant in Caracas, Venezuela, as saying that one of the men who had planted the bomb called Bosch afterward with the message, “A bus with 73 dogs went off a cliff and all got killed.”

Earlier this month, Posada was acquitted in El Paso, Texas, of perjury, obstruction and immigration fraud charges in connection with his return to the U.S. in 2005.

Though he was acquitted in the airline attack, there is little doubt that Bosch was behind other terrorist acts in the decade after the 1959 Cuban revolution. In recommending in 1989 that he be deported, the Justice Department said he had committed 30 acts of sabotage in the United States, Puerto Rico, Panama and Cuba from 1961 through 1968.

An exile group he headed claimed responsibility for 11 bombing attacks against Cuban government properties.

Orlando Bosch Avila was born on Aug. 18, 1926, in the village of Potrerillo, about 150 miles east of Havana. He went to medical school at the University of Havana, where he was president of the student council. He worked on student issues with Castro, the law school’s delegate to the council, then cooperated with him in fighting the dictatorship of Fulgencio Batista.

Bosch did his medical internship in pediatrics at the University of Toledo, in Ohio, starting in 1952, then returned to Cuba to practice medicine. He vaccinated children against polio and organized clandestine support for Castro. But he became disillusioned with the revolution and in June 1960, less than 18 months after Castro came to power, Bosch fled to Miami with his wife, Myriam, and four children.

He worked for a hospital in Coral Gables, Fla., bought a beat-up blue Cadillac, took a liking to the television show “Mission: Impossible” and settled into American life. But his anti-Castro passion became consuming and he was fired for storing explosives on the hospital grounds. He was arrested on charges of towing a homemade radio-operated torpedo through traffic. Federal agents charged him and five others with trying to smuggle 18 aerial bombs out of the country.