"My soul aches," Arreaga, 56, told a news conference, his voice breaking. "These governments we live with are unjust ... they do nothing to watch over the common good. They call it the government of change; it's just changing the horse's rider."

He had pledged in jail that he would not back down in his campaign to protect the Sierra Madre mountains in Guerrero state from irresponsible logging. But on Monday, still clearly shaken by his ordeal, he said he would decide his future day by day.

"For me it was like 10 years," he said about his 10 months in jail, where inmates went days without water and a fatal fight might erupt over a tortilla. "I never thought I would come to this doing nothing more than caring for the forest."

He was jailed in November for the 1998 murder of the son of a powerful local landowner who rights workers say has benefited from logging in a forest decimated by cutting.

A judge last week found that the charges were false and evidence had been fabricated, in a ruling lauded by rights activists as a step forward for justice.

Still, Greenpeace, Amnesty International and other groups said Arreaga's unjust imprisonment made him a symbol of a system that often puts police, prosecutors and courts at the service of political leaders, especially in the countryside.

And it was further proof of the government's total abandonment of its forests in a nation that ranks fifth worldwide for deforestation, said Alejandro Calvillo, director of Greenpeace in Mexico.

"TERRIBLE THINGS"

Arreaga's wife, Celsa Valdovinos, a leading environmental activist in her own right, said the family feels threatened.

"We want to keep working, but it's dangerous," she said. "I am afraid because terrible things have happened."

Fox was elected in 2000, ending 71 years of rule by the authoritarian PRI party. He pledged to reform justice but his proposals have stalled in Congress and experts say the system is still rife with corruption and rights abuse.

Arreaga helped found the Peasant Ecologists of the Petatlan Sierra, a group celebrated internationally for blocking corporate logging off the Pacific coast in the 1990s.

He was the latest in a line of members arrested or charged in what their supporters say were bogus cases engineered by local political bosses, or caciques, who hold sway with the military, police and courts.

Arrest orders for another 13 members of the group for the same murder remain in effect. Rights groups want the charges dropped and the ecologists protected from persecution.

Activists also want local prosecutors and Arreaga's accusers investigated for bringing false charges. And they called for the investigation of a shooting attack on another member and his family in May that killed two of his sons.