Jose Rodrigues Moreira, a Brazilian man accused of conspiring to kill two environmental activists, has been acquitted, as two other men were found guilty.
The jury set Moreira free on Thursday due to insufficient evidence, disappointing family members of the murdered married couple who claim he was the alleged mastermind of the attack and has enjoyed impunity.
Jose Claudio da Silva and his wife, Maria do Espirito Santo, had for years campaigned against loggers and ranchers who force slave labour to clear-cut large swaths of the Amazon.
They had reported illegal loggers to police and federal prosecutors, and were killed in a May 2011 ambush near the Amazonian town of Maraba.
Two men, Lindonjonson Silva Rocha and Alberto Lopes do Nascimento, were found guilty of killing the couple and sentenced to more than 40 years in prison each.
"This is a clear defeat for the families of the victims," said Al Jazeera's Gabriel Elizondo, reporting from the court. "This was the person they really wanted to see go to jail.
"There are about 100 people outside the court; family members, friends, acquaintances. They're all chanting 'justice' and 'crime'."
Prosecutors vowed to appeal the acquittal of Moreira.
Killers 'enjoy impunity'
Prosecutors accused Moreira of ordering the killings because the Silvas opposed the eviction of three families occupying his land in the Nova Ipixuna reserve.
"The verdict was to a certain point a positive one because those who shot the guns were convicted," said Edmundo Rodrigues Costa, the national coordinator of the Catholic Land Pastoral watchdog group that tracks land-related violence.
"But the verdict unfortunately again showed that those who order people killed enjoy impunity," he said.
Moreira and the two men convicted were arrested in a jungle hideout 300km from Maraba in the northern state of Para after the attack.
The murder was the first in a series of 10 over a three-month period in the Amazon, most of them in Para.
Para is among Brazil's most violent and lawless states, notorious for land-related violence, contract killings, slave-like labour conditions and wanton environmental destruction.
Last month, the Land Pastoral said the number of rural activists killed in the country rose 10 percent from 2011 to 2012, with most deaths occurring in the Amazon region.
It said in a report that illegal logging and the resulting conflicts were responsible for the majority of the 32 slayings of local activists in Brazil last year.
In Brazil, killings over land are common and seldom punished, as powerful landowners clash with farmers and others for control of lucrative farming and logging land.
The slayings are mostly carried out by gunmen hired by loggers, ranchers and farmers to silence protests over illegal logging and land rights in the environmentally sensitive region.