(CNN) Prosecutors placed former Brazilian President Luiz Inacio Lula da Silva under formal investigation Wednesday, state media reported.
The Sao Paulo's prosecutor's office presented charges against Lula, state-run Agencia Brasil said. The charges must be accepted by a judge for the case to proceed.
Federal prosecutors have alleged that Lula da Silva benefited from a bribery scheme involving state-owned oil company Petrobras while he was President and after leaving office. Lula da Silva faces several charges, including money laundering, according to Agencia Brasil.
He has staunchly denied the allegations.
Police questioned Lula da Silva and searched his home on Friday.
On Wednesday, his lawyer and an institute he founded criticized the way authorities are handling the case, accusing prosecutors of bias, according to Agencia Brasil.
Attorney Cristiano Zanin Martins told state media that the investigation was not impartial and was the result of "deliberate intention to tarnish the image of Lula."
Authorities think construction companies made large payoffs to Petrobras executives and politicians in exchange for lucrative contracts. Among other things, investigators are looking into whether these funds were used to pay for a luxury triplex and a country home believed to have been used by Lula da Silva. They're also investigating any payments, donations to the Lula Institute and speaking fees made by construction firms to the former President.
The Lula Institute responded defiantly Friday to what it called authorities' "arbitrary, illegal and unjustifiable" actions, insisting that Lula da Silva "never concealed assets or received undue advantage" before, during or after his presidency.
"The only (purpose) ... is to subject the former President to public embarrassment," the Lula Institute said of the anti-corruption investigation known as Lava Jato. "It is not Lula's credibility that is compromised when its leaders turn to a political target in the most fragile pretext."
The intense, extensive probe threatens the storied legacy of one of Brazil's most famous and most revered politicians.
Lula da Silva helped found the leftist Workers' Party in the early 1980s, then successfully ran for a seat in Brazil's national legislature later that decade. He lost his first three presidential runs before finally breaking through with a win in 2002's election. He served two terms as Brazil's President, from January 2003 to 2011.
Party officials have said they hope he'll run again for the nation's top job in 2018.