An ex-director of Brazil's state oil giant Petrobras at the center of a scandal after accusing dozens of politicians of taking oil deal kickbacks, gave nothing away in a hearing Wednesday.
"I reserve the right to remain silent," Paulo Roberto Costa, who headed Petrobras' refining and supply unit between 2004 and 2012, told the public congressional hearing -- though commission members insisted on questioning him anyway.
His allegations that more than 50 lawmakers -- mainly from the ruling Workers Party (PT) -- received billions in under-the-table deals have made waves as Brazil approaches an October 5 presidential election.
The purported links to the PT have left President Dilma Rousseff fighting to see off the challenge of environmentalist and former party ally Marina Silva, with the pair running neck-and-neck in latest polling.
Polls give Silva, a former environment minister, a narrow lead for an October 26 run-off vote.
Lawmakers on the commission asked Costa if he had been involved in the controversial purchase of the Pasadena, Texas, oil refinery, which Petrobras bought for $1.2 billion from Belgian-based Astra oil just a year after the latter had paid only $42.5 million for the facility.
They also wanted to know if he had made his allegations as part of a plea bargaining bid given that he faces decades in jail on money laundering charges.
He simply responded: "With all due respect I have nothing to say."
Previously, media reports had quoted the white-haired Costa, who arrived at the Congress building in Brasilia amid tight security, as saying: "There was a politician knocking at my door every single day."
Among the government allies Costa has accused of taking bribes are the president of the senate, Renan Calheiros, and the leader of Congress' lower chamber, Henrique Eduardo Alves, both of the center left PMDB.
He also named former opposition presidential candidate Eduardo Campos, who was killed in an August 13 air crash, leaving his Socialist Party (PSB) to ask former running mate Silva to stand in his place.
Those Costa has named have roundly denied wrongdoing.
The PT and PMDB backed a public commission session saying they have nothing to hide.