An internal investigation of Petrobras' controversial $1.1 billion purchase of a Texas refinery is nearing completion, the Brazilian state oil giant's chief said. The growing scandal surrounding the purchase has bedeviled not only the Brazilian government but also President Dilma Rousseff, who is seeking reelection on October 5. Rousseff was on the Petrobras board when it gave the green light in 2006 to the acquisition. Astra bought the refinery for just $42.5 million in 2005. Petrobras Chief Executive Graca Foster on Monday said the probe was "near its end," and that she expected a report and conclusions on June 6. Foster meanwhile has been cooperating with Brazilian federal police as authorities investigate a broader alleged $4.5 billion money-laundering operation inside the oil firm. A former Petrobras executive, Paulo Roberto Costa, was arrested in late March as part of the ongoing broader probe known as the Lava Jato Operation. That 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.