Brazil's Supreme Court has freed a man awaiting trial on charges of orchestrating the murder of a Catholic nun and activist, Dorothy Stang.
Dorothy Stang spent decades defending peasant farmers
In a three-to-two vote, the Court decided keeping Regivaldo Pereira Galvao in custody violated his rights.
The decision has been decried by the family and supporters of Ms Stang, who say he might abscond or try to intimidate witnesses.
Ms Stang spent 30 years campaigning for peasant rights and against logging.
The 73-year-old from Dayton, Ohio, was found on a muddy track in the rainforest, shot six times, in February 2005.
The death followed a long-running dispute with ranchers over a patch of forest which they wanted to clear for pasture land, and Ms Stang wanted declared a sustainable development reserve.
Three men have already been jailed for Stang's murder
Three men have already been convicted over her murder - two gunmen and one intermediary.
During those trials testimony was given that Mr Galvao, along with another rancher Vitalmiro Moura, ordered and paid for Ms Stang to be killed. Both men have been charged but have yet to face trial.
Mr Galvao has been in custody pending trial since April 2005, but on Thursday Brazil's Supreme Court ruled his pre-trial imprisonment illegal and ordered his immediate release.
The judges threw out a previous ruling that his detention was necessary to preserve public order.
"I am dumbfounded," Ms Stang's brother David Stang told the Associated Press news agency from his home in Colorado.
"This is a man whose involvement in the killing has been documented in a trial. There's no doubt about his duplicity.
"My sister loved Brazil, she loved the Amazon, she loved the constitution. This decision is an insult to her and to the family."
Other supporters say they are concerned Mr Galvao could disappear, as suspects in similar cases have done in the past, or could threaten witnesses.
More than 750 land activists are thought to have been killed in the Amazonian state of Para in the last three decades, but only nine killers have been convicted.
Convictions for those who orchestrate such killings are even rarer.
This is often blamed on corrupt links between the region's landowners and loggers on one hand, and police and politicians on the other.