Vitalmiro Bastos de Moura had been tried three times before and sentenced to up to 30 years in prison, but his lawyers appealed and the Supreme Court annulled Moura's latest conviction. The high court said he wasn't given enough time to prepare his defense during the 2010 trial.
The state prosecutor's office said the 43-year-old Moura is in the same prison he's been held in since 2010.
Local media quoted Stang's brother David, who was present at the trial, as saying: "Justice has been made. I am very happy."
Phone calls and an emailed request for comment from David Stang went unanswered Friday.
Prosecutors contend that Moura and another rancher hired gunmen to kill Stang. The defense said there wasn't enough evidence linking Moura to the crime and planned to appeal.
After beginning Thursday morning, the lightning-quick trial ended late that night in a state court in Belem, the capital of the violence-wracked Amazonian state of Para. State prosecutors said the trial moved quickly because it was Moura's fourth and most of the legal processes had been taken care of in previous trials.
Regivaldo Galvao, another rancher also charged with planning Stang's murder, was sentenced to a 30-year jail term in 2010. Last year, the Supreme Court ordered his release, saying he had the right to remain free pending the outcome of his appeal process.
Earlier this year, Stang's confessed killer was released from prison after serving less than nine of the 27 years he was sentenced to. A Para state judge said Rayfran das Neves Sales was entitled to serve the rest of his sentence under house arrest.
Another man charged with taking part in Stang's killing is in prison, and a fifth suspect is at large.
Stang was born in Dayton, Ohio, and spent three decades trying to preserve the rain forest and defend the rights of poor settlers who confronted powerful ranchers seeking their lands in the Amazon's wild frontier. Stang was gunned down with six shots fired at close range from a revolver.
The northern Brazilian state of Para is notorious for land-related violence, contract killings, slave-like labor conditions and wanton environmental destruction.
More than 1,200 activists, small farmers, judges, priests and others have been killed over attempts to preserve the rain forest in the last two decades, according to the Catholic Land Pastoral, a watchdog group that tracks rural violence in Latin America's largest nation.
The killings are mostly carried out by gunmen hired by loggers, ranchers and farmers to silence protests over illegal logging and land rights. Yet killings over land are seldom punished.
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