Brazil's Petrobras has turned over documents requested in an investigation into a $4.5 million money-laundering operation, the latest in a series of problems to plague the state oil giant. Petrobras CEO Graca Foster supplied federal police with the documents Friday. "A number of documents were recovered and more than 70,000 reais ($31,500, 22,700 euros) was seized," the police said, adding that further details would not be released until a final report on the operation is filed. A total of 23 search and arrest warrants were issued Friday, to be carried out in the Brazilian cities of Sao Paulo, Campinas, Rio de Janeiro, Macae and Niteroi. Police said they were able to execute 16 of these, including one arrest, although a second wanted person eluded capture. Four other individuals were brought in to testify before the justice system. A former Petrobras executive, Paulo Roberto Costa, was already arrested in late March as part of the ongoing investigation, known as the Lava Jato Operation. Federal police did not explain what the documents taken from Petrobras were related to. The state oil giant, however, said they concerned a contract. 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 President Dilma Rousseff, who is up for re-election later this year. The Brazilian 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.