The lone suspect in the killing of an independent U.S. journalist during protests against the Oaxaca state government three years ago was let out of prison Thursday for lack of evidence.

Juan Manuel Martinez, who had been one of the protesters seeking the ouster of the governor, called himself a political prisoner and said the 16 months he spent in jail were the worst "torture of my life."

His lawyer, Alba Cruz, had said Wednesday that a Mexican federal court cleared Martinez and ordered his release.

Many human rights groups contend Martinez was wrongly charged with the slaying of Bradley Will, 36, of New York.

Will was shot in October 2006 as he videotaped a clash between protesters and government supporters in the southern state. He was covering the conflict for Indymedia.org.

Martinez was charged with homicide. Two others were charged with covering up the crime, but were later released. All three are supporters of the radical movement known as the People's Assembly of Oaxaca, or APPO, which seized control of Oaxaca city for almost five months pushing for the removal of Gov. Ulises Ruiz.

The fight started as a teachers strike and ballooned into a broader movement to demand Ruiz's resignation over allegations he rigged his election victory.

Critics said prosecutors ignored evidence that implicated Ruiz's supporters. Prosecutors have failed to give specifics about the ballistics evidence or explain why Martinez would have shot Will, who supported the protest movement.

"I'm happy to have gained my freedom and that government's injustice against me and my family has ended," Martinez said after he and other APPO members marched from the prison to the main square in Oaxaca city. "What happened to me is what happens to all political prisoners."

Will's family also has criticized the investigation into the journalist's slaying and say they believe pro-government forces were responsible.

Amnesty International urged Mexican authorities to continue looking for Will's killer.

Martinez's release was long overdue, said Kerrie Howard, director of the London-based Amnesty's Americans program. "Mexican authorities used Juan Manuel as a scapegoat to demonstrate progress in the death of Brad Will."