Three suspected killers of a couple who protested illegal logging in the Brazilian Amazon have gone on trial.

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.

The couple were killed in a May 2011 ambush near the Amazonian town of Maraba.

Antonio Filho, a member of Brazil's Catholic Church-affiliated Pastoral Land Commission (CPT) who is monitoring the trial, said Wednesday’s trial would last until the following day.

Jose Rodrigues Moreira, the alleged mastermind of the attack, and the two alleged perpetrators Lindonjonson Silva Rocha and Alberto Lopes do Nascimento, were arrested in a jungle hideout 300 kilometers 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, one of the Brazilian states hardest hit by violence by local loggers and ranchers against rural workers and their supporters.

A report by the CPT said big landowners in the area often enjoy "total impunity".

At the time of the killing of da Silva and his wife, Amnesty International, the London-based rights watchdog, had called on Brazilian authorities to end these killings as well as "the impunity enjoyed by those who incite this violence".

Several Amnesty International representatives were due in Maraba Wednesday to monitor the trial.