RIO DE JANEIRO -- A Brazilian rancher accused of ordering the murder of U.S. nun and Amazon defender Dorothy Stang was found guilty and sentenced to 30 years in prison.

Jurors in the jungle city of Belem reached the decision late Monday after 15 hours of deliberations, according to a statement on the Web site of a Para state court.

The case was seen as a test of Brazil's ability to battle the near absolute impunity that reigns in the largely lawless Amazon region -- whether it be the murder of activists or halting illegal deforestation.

In the last two decades, more than 1,200 people have been killed in land conflicts across Brazil, mostly in the Amazon region, according to the Catholic Land Pastoral, a watchdog group that tracks rural violence in Latin America's largest nation.

Prosecutors said Vitalmiro Moura ordered the 73-year-old Stang's killing in 2005 because she blocked him and another rancher from taking over land the government gave to farmers.

His guilty verdict makes him the only so-called "mastermind" behind the killing of such activists, landless farmers and others defending the rights of the poor in the Amazon, to be imprisoned for the crimes, the Catholic Land Pastoral said.

About 80 of the gunmen who prosecutors say were paid by powerful ranchers to carry out the slayings are behind bars.

Stang was a Dayton, Ohio, native who worked for three decades to preserve the rain forest and defend poor settlers' land rights.

"We've waited so long for this verdict," said nun Rebeca Spires, who has worked in Brazil for four decades and knew Stang for 35 years. "This conviction sends a strong message to the other masterminds that the impunity is ending."

Spires said it was a milestone victory for environmental and other activist groups in the Amazon. Because there is an "endless supply" of gunmen available for hire, it will take convicting the rich ranchers who are behind the killings to end the violence, she said.

Moura was previously convicted of Stang's murder and then acquitted in an automatic retrial. That decision was overturned last year on a technicality, however.

Confessed gunman Rayfran das Neves Sales is serving a 28-year sentence for the crime.

Regivaldo Galvao, the other rancher prosecutors say helped orchestrate Stang's murder, is scheduled to face trial at the end of this month.