Brazilian police arrested former senator Gim Argello and launched raids in three states on Tuesday as part of a massive corruption investigation centered at state-run oil firm Petrobras, federal prosecutors said.
The 28th round of police raids in the so-called "Operation Car Wash" was based on evidence that Argello took bribes to ensure executives at major infrastructure companies would not be called to testify at a congressional committee in 2014, prosecutors said.
"These are alarming facts because they strongly suggest that a congressional investigative committee, which has an important role in our democracy, was used by a senator for corruption instead of fighting it," prosecutor Athayde Ribeiro Costa said in the statement.
The two-year investigation has uncovered systemic corruption across multiple companies, including state-run oil producer Petroleo Brasileiro SA , and the highest levels of government since the Workers' Party took power in 2003.
The probe has given powerful momentum to impeachment proceedings against President Dilma Rousseff, even though she herself is not being investigated.