Nearly a month after the murder in Brazil\'s Amazon of an activist couple believed to have been threatened by land and logging barons, the investigation has gone nowhere. The killing of the activists, who had denounced illegal logging, was the latest in a string of deadly attacks on environmentalists, murders allegedly linked to powerful corporate interests in the vast South American jungle. Jose Claudio Ribeiro da Silva, 52, and his wife Maria do Espirito Santo da Silva, 51, were shot dead in an ambush in late May close to their home in Nova Ipixuna, a small town of 15,000 people in the state of Para. Since their deaths, another three activists have been killed in the state, which is the epicenter of deadly land disputes. A fourth was killed in the state of Rondonia, also in the vast Amazon jungle. Junior, a 30-year-old agronomist who worked for two years with Silva and declined to give his last name for fear of retribution, said the murdered ecologist had received death threats. \"He was told things like \'Your days are numbered\', \'You are going to die\' and \'Get ready to be silenced forever\',\" Junior told AFP, accusing \"powerful landowners and forest companies\" of contracting the murders. \"They went to his place several times to kill him. He went out to challenge them. They didn\'t kill him because they wanted to kill his wife as well. In the end, they succeeded,\" he said, visibly shaken. The slain couple were part of the National Council of Gatherers, a group that collects natural food from the Amazon. It was founded by an ecologist, Chico Mendes, who was murdered in 1988. The Para prosecutor\'s office said the Silvas\' murder \"had a detail suggesting it was a typical hit: the killers cut off one of Jose Claudio\'s ears.\" \"In the Amazon region, hired killers do exist,\" said Jose Battista, a lawyer for the local branch of the Pastoral Land Commission, a group linked to Brazil\'s Catholic Church that defends poor rural workers. Last year, the Commission printed a list of 125 people it said had contracts on their heads. Thirty of them were in the state of Para, and the Silvas were among them. \"Since the start of the year, we already have 20 names\" to add to the list of those under threat of murder, Battista said. Brazilian President Dilma Rousseff vowed the day after the couple\'s death that the perpetrators would be brought to justice and sent a special military force to the region because of state officials\' record of doing nothing in the face of such violence. But to date, the police have made no progress in the case. \"The absence of government has led to illegal deforestation,\" said Valdimir Ferreira, a municipal councillor in Nova Ipixuna. \"Jose Claudio started a fight, a war against the loggers and powerful farmers. That\'s why I can state that his death was ordered by them.\" The mayor of the town, businessman Edson Alvarenga, disagrees. \"The murders could be the result of internal conflict in the community,\" he said. \"I\'ve heard that the one who killed him is someone from here, in the community.\" Junior allowed that there were local conflicts \"because some people want to sell their plot of land.\" \"But I can assure you that it was loggers or farmers who gave the order to have him killed,\" he said.