(CNN) -- Rene Gonzalez, a Cuban convicted of spying in the United States, was released Friday after serving most of a 15-year sentence, a prison spokesman told CNN.
Gonzalez was one of five convicted spies known as the "Cuban Five" who were arrested in 1998.
A Miami jury in 2001 convicted members of what was called the Wasp Network on charges they had spied on prominent Cuban-American exile leaders and U.S. military bases.
The five were Gonzalez; Ruben Campa, also known as Fernando Gonzalez; Gerardo Hernandez; Luis Medina (also known as Ramon Labanino); and Antonio Guerrero.
Hernandez, the group's leader, also was convicted of conspiracy to commit murder for engineering the shoot-down of two planes flown by the group Brothers to the Rescue in 1996.
Gonzalez is the first of the five to be released from prison. He was behind bars for 13 years and 26 days, said his attorney, Philip Horowitz.
But he still has three years of probation to serve, said Neil Robinson, spokesman for the federal prison in Marianna, Florida.
Gonzalez was freed about 4 a.m., Horowitz said.
"I cannot discuss or disclose what he is doing and where he is going in order to protect his personal safety," he said. "Mr. Gonzalez is glad to be out but it is a bittersweet day because his four friends are still in prison. He wishes he could return to his family in Cuba as quickly as the judge permits."
Gonzalez will appeal the conditions of his probation so that he may serve it in Cuba instead of the United States, Horowitz said.
Gonzalez has a 25-year-old daughter and a 13-year-old daughter who was only 4 months old when he was arrested.
During the trial, the defendants claimed they had spied as a way to defend Cuba from hardline anti-Castro groups in Miami they feared would attack the island.
The case has been widely followed in Cuba, where the men were regarded as heroes and whose former leader, Fidel Castro, regularly advocated their release.
Gonzalez was born on Chicago's north side in 1956, but his parents brought him to their native Cuba in 1961 so that the family could join Castro's revolution.
U.S. authorities accused the Wasp Network of spying on an American naval base in Key West, Florida, and militant anti-Castro Cuban groups in Miami.
Throughout Cuba, Gonzalez and the four other convicted spies are considered "political prisoners," unjustly punished in American courts.
They are known simply as "Los Cinco," or the Cuban Five, and their faces appear on billboards.
State-controlled Cuban media labels them "terrorism fighters" because they infiltrated Cuban-American groups in South Florida that the Cuban government alleges was bent on terrorizing the island in the 1990s.
That era marked severe financial difficulties for Cuba because the country lost subsidies from the collapsed Soviet Union. The Cuban government renewed its tourism sector to bring in hard cash.
But several Cuban tourist destinations were bombed during that decade, and the Castro regime lodged a protest with the United States over what it claimed were Cuban exiles in America financing the attacks.
CNN's Michael Martinez, Gustavo Valdes and Bill Mears contributed to this report.