Brazil's president on Monday promised authorities would carry out a thorough and complete probe of alleged money laundering at state oil giant Petrobras. "Whatever needs to be investigated will be, to the fullest extent of the law; and whoever needs to be punished will be, to the fullest extent of the law," G1 news quoted Dilma Rousseff as saying. On Friday, Petrobras Chief Executive Graca Foster supplied federal police with documents sought by authorities investigating the alleged $4.5 billion money-laundering operation. Federal police did not explain what the documents were related to. Petrobras, however, said they concerned a contract. A former Petrobras executive, Paulo Roberto Costa, was arrested in late March as part of the ongoing probe known as the Lava Jato Operation. The investigation is only the latest in a long series of problems to plague Petrobras, which has lost billions of dollars in market value over the past five years. A growing scandal surrounding its controversial purchase of a Texas refinery, which came at a ballooned price of $1.1 billion has bedeviled not only the Brazilian government but also Rousseff. The opposition has urged the creation of a legislative commission to investigate the purchase. Meanwhile, Brazilian lawmakers announced the formation of a committee in March to investigate alleged kickbacks made to Petrobras officials by Dutch firm SBM Offshore, in return for preferential treatment for contracts.