President Joao Goulart to be exhumed 13 November 2013 Last updated at 14:53 The remains of a former president of Brazil, Joao Goulart, will be exhumed on Wednesday to establish whether he died of natural causes or was poisoned. Mr Goulart, widely known as Jango, died in 1976 in exile in Argentina. His cause of death was deemed to have been a heart attack. But a former Uruguayan intelligence officer has said Mr Goulart was poisoned by agents working for the region's military governments. He governed from 1961 to 1964. Forensic scientists commenced work on Wednesday morning, digging a hole in the grave to create an escape for gases which had formed inside the tomb. Mysterious death Mr Goulart, a progressive leader with left-wing sympathies during the height of the Cold War, was deposed in the 1964 military coup. He fled first to Uruguay, where he settled as a farmer, and in 1973 to Argentina on the invitation of its president, Juan Peron. Mr Goulart was found dead on 6 December 1976 in the Argentine city of Mercedes, nine months after a military junta had overthrown the government of Juan Peron's widow, Isabel Peron. Officials at the time said he had died of a heart attack, but no post mortem examination was carried out by the authorities in either Argentina or Brazil, where he was taken for burial. Doubts about his death resurfaced five years ago when a former Uruguayan intelligence officer serving a sentence for drug smuggling in Brazil alleged Mr Goulart was poisoned by Uruguayan agents at the request of Brazilian military rulers. New chapter The intelligence officer, Mario Neira, said the alleged murder was part of Operation Condor, a plan under which the military governments of Argentina, Bolivia, Brazil, Chile, Paraguay and Uruguay collaborated to eliminate their political opponents in the 1970s and 80s. Neira alleges that Mr Goulart died after his heart medication was swapped with one altered to cause a cardiac attack, by agents working on behalf of the Brazilian military. Brazil's National Truth Commission, which started work last year, agreed to investigate the claims with the help of the presidency's human rights commission. "Today we will open a new chapter in the tale of mystery which has surround the death 37 years ago of the former president," the human rights commission said in a statement. "The exhumation will put an end to the anguish of his family and thousands of Brazilians who have sufficient reason to believe that his death did not occur spontaneously, as stated in the death certificate - which was issued without a prior post mortem examination," they added. The former president's grandson, Joao Marcelo Goulart, said it was "a historic moment not just for the family but also for the country and all the relatives of those killed, disappeared, tortured and exiled by the military dictatorship." Mr Goulart's remains will be removed from the family pantheon in Sao Borja, a small Brazilian town near the Argentine border. Local media say they will then be taken to the capital, Brasilia, where an official ceremony is planned to make up for the fact that Mr Goulart was the only Brazilian president to be buried without the honours usually given to a former head of state. Toxicology tests will be carried out on the remains and sent abroad to be analysed, local reports say. Up to 500 people were killed or disappeared under Brazil's military rule - a far lower number than in shorter periods of military rule in neighbouring Argentina and Chile. But thousands of Brazilians were tortured, exiled or deprived of their political rights.