July 24 (Reuters) - Prosecutors and federal police in Brazil unearthed the country's largest-ever corruption scandal by tying a ring of black-market money changers to a price-fixing and political kickback scheme at state-run oil firm Petrobras .
Executives from two dozen engineering firms are accused of inflating the value of service contracts and funneling the excess funds into their own bank accounts and to political parties, including President Dilma Rousseff's Workers' Party.
On Friday, prosecutors presented formal charges against the chief executive officer of Latin America's largest engineering firm, Odebrecht SA, and other senior executives who were arrested on June 19.
Below are key moments of Brazil's largest-ever corruption investigation, which prosecutors in the southern city of Curitiba expect to continue for another two years. A separate investigation into politicians is also advancing in Brasilia.
March 20, 2014
Federal police arrest the former head of Petrobras' refining and supply department, Paulo Roberto Costa, the result of an investigation that started when they noticed Costa had been given a Range Rover by convicted money changer Alberto Youssef.
Aug 22, 2014
Costa signs a plea bargain deal with prosecutors, agreeing to explain the corruption scheme and name beneficiaries in exchange for a lighter sentence. Plea bargain deals become a cornerstone of the investigation.
Nov 14, 2014
Federal police arrest 18 people including former Petrobras engineering and services director Renato Duque and senior engineering executives, the first broad raid of the investigation.
Dec 11, 2014
Prosecutors in Curitiba formally charge 36 people, 22 of them from engineering firms OAS , Camargo Correa, UTC Engenharia, Galvao Engenharia, Mendes Junior and Engevix. Prosecutor Deltan Dallagnol declares war on corruption in Brazil in a nationally televised press conference.
Dec 29, 2014
Petrobras bans 23 suppliers cited in investigation from bidding in future tenders.
Aldir Bendine, former head of state-run Banco do Brasil SA, steps in as Petrobras CEO after Maria das Graças Foster and other senior leaders abruptly resign.
Brazilian prosecutors file lawsuits against six construction and engineering groups, seeking over $1 billion in damages related to contract fixing, bribery and political kickbacks.
Brazil's Supreme Court says it will investigate the speakers of both houses of Congress and 32 other sitting politicians in connection with the Petrobras scheme. Twelve senators and 22 congressmen from five parties are under investigation, all but one from President Rousseff's governing coalition.
Brazilian police arrest the treasurer of the ruling Workers' Party, João Vaccari, moving the investigation closer to Rousseff's inner circle. Vaccari resigns to focus on his defense.
Paulo Roberto Costa is sentenced to 7 years and 6 months in prison, but will only serve one year of house arrest due to his collaboration and time already spent in detention. A total of eight people are convicted in the probe's first sentences.
After lawyers fiercely contest the legality of lengthy pre-trial jailings in Curitiba, the Supreme Court overrules federal judge Sergio Moro and orders nine executives to be released on house arrest.
Nestor Cervero, former international director of Petrobras, is sentenced to five years in jail for money laundering.
Brazilian police arrest the chief executives of the country's two largest construction companies, Marcelo Odebrecht, head of family-run conglomerate Odebrecht SA, and Otavio Marques Azevedo, CEO of Andrade Gutierrez. Prosecutors say the companies led the cartel of engineering firms.
Weekly magazine Veja publishes plea bargain testimony from Ricardo Pessoa, head of UTC Engenharia, without saying how it obtained the documents. Pessoa said money from the overpricing of contracts was donated to Rousseff's 2014 re-election campaign, allegations she and her party deny.
Police arrest Jorge Zelada, former director of Petrobras' international division. Prosecutors said he appeared to have received bribes on a contract for the Titanium Explorer drillship operated by Vantage Drilling Co and another rig operated by Pride International, a company acquired by Ensco Plc in 2011. Vantage and Ensco say they have found no evidence of wrongdoing. More than a dozen foreign firms are thought to have paid bribes to win Petrobras contracts.
Federal police carry out search and seizure operations at the home of Senator and former President Fernando Collor de Mello, the first such operation targeting a sitting politician.
In a separate investigation, federal prosecutors open a formal inquiry into whether former President Luiz Inácio Lula da Silva improperly used his connections overseas to benefit Odebrecht after leaving office.
Three executives of Brazil's Camargo Correa group are convicted of money laundering, corruption and other charges, the first construction-industry executives to be sentenced in the Petrobras investigation. Two executives will serve a year of house arrest with electronic monitoring and two to six years of modified house arrest while the third could face nine years and six months in prison. (Reporting by Caroline Stauffer)