In 2014, the largest corruption scandal in the history of Brazil was uncovered centered around Petrobras. Initially, the investigation was not focused on Petrobras executives, but rather small time doleiros (black market money dealers), who mostly used small businesses to carry out their transactions. The investigation discovered links to an executive at Petrobras, , the director of refining and supply. President Dilma Rousseff made one critical change in policy, the introduction of plea bargains, making it possible to offer deals in exchange for information leading to further arrests. It was a defining moment of the investigation. Costa later confessed that he and his colleagues had knowingly overpaid on contracts, funneling excess funds to personal accounts. Paulo Costa received kickbacks of 3% on all contracts. According to the investigation, a small number of top Petrobras officials colluded with an organized cartel of 16 companies to overcharge Petrobras for construction and service work in return for bribes and kickbacks. Petrobras officials pegged the total of all bribes at $2 billion at minimum. As of August 2015, 117 indictments had been issued, five politicians arrested, and criminal cases brought against 13 companies. Both Dilma Rousseff, who promised to cut corruption in her election campaign, and former Brazilian president Luiz Inácio Lula da Silva served on the board of directors of Petrobras during the scandals and both were blamed, as well as the president of the lower house, Eduardo Cunha. Cunha was sentenced in March 2017 to 15 years in prison.