A Brazilian court on Thursday began the re-trial of the reputed mastermind of U.S. nun and environmental activist Dorothy Stang's 2005 murder.

This is the fourth trial of land baron Vitalmiro Bastos de Moura in a case that has deeply affected Brazil.

Convicted in May 2007, he was given a second trial under a law that automatically provides for new proceedings if a sentence exceeds 20 years.

That second trial, concluded in May 2008, undid the conviction, but prosecutors appealed to a higher court, which threw out the acquittal in April 2009 and ordered Moura re-arrested.

The third trial resulted in the re-instatement of the original conviction and a 30-year sentence for the landowner, though he has been allowed to serve his time under a relaxed, partially custodial regime.

Moura returned Thursday to a courtroom in Belem, the capital of the Amazon region state of Para.

Prosecutors accuse Moura of ordering Stang's murder in collaboration with another big landowner, Regivaldo Pereira Galvão, who was sentenced in 2012 to 30 years behind bars.

In Thursday's court session, eight witnesses are scheduled to testify, three of them for the prosecution and five for the defense.

Stang, 73, who worked for years to defend landless peasants and protect the environment in Amazonia, was shot six times at point-blank range on Feb. 12, 2005.

Confessed shooter Rayfran das Neves Sales is serving a 27-year sentence, while two other defendants were sentenced to 17 and 18 years in prison, respectively.

The Ohio-born Stang, a member of the Franciscan Sisters of Notre Dame de Namur, settled in Brazil in the 1970s and distinguished herself by working to defend the Amazon against exploitation by industry, logging interests and landowners.

Stang's murder prompted then-President Luiz Inacio Lula da Silva to send 2,000 troops to Para to deal with violent land disputes that have claimed more than 700 lives over the last 30 years. EFE