Brazil's highest-profile corruption scandal trial has begun with dozens of former officials facing vote-buying charges in a case that could tarnish the legacy of popular ex-leader Luiz Inacio Lula da Silva.
In what the media has dubbed "the trial of the century", 38 former ministers, legislators, businessmen and bankers face prosecution before the Supreme Court over alleged vote-buying in Congress between 2002 and 2005.
Supreme Court Justice Carlos Ayres Britto opened proceedings on Thursday by naming each defendant and detailing the charges, which range from embezzlement and money laundering to corruption and fraud.
Those found guilty face up to 45 years in prison.
Known as "Mensalao" or big monthly payments, the scandal embroils senior members of Lula's Workers Party (PT) and Brazil's ruling coalition, but more broadly sheds light on the now-reviled practices of the entire political establishment.
Lula, the founder and leader of the leftist party who first took office in January 2003, followed in office by fellow PT member Dilma Rousseff in January 2011, is not among the defendants.
According to charges that first surfaced in 2005, during Lula's first term, PT members allegedly offered bribes to members of Congress in exchange for their votes.
Prosecutors allege that the bribe money was skimmed from the advertising budgets of state-owned companies through a company owned by businessman Marcos Valerio de Souza, one of the accused.
None of the 38 have been arrested or appeared in court and Lula, now 66 and recovering from throat cancer, said Thursday that he would not follow the proceedings.
"The attorneys are the ones that have to be there," he told reporters in Sao Paulo.
The ex-president has maintained that he was betrayed and offered public apologies on behalf of the PT.
The party denied any vote-buying or Mensalao payments in a statement ahead of the trial.
A lawyer for PT lawmaker Roberto Jefferson, who exposed the vote-buying scheme in 2005, said he would ask during the trial why Lula is not among the accused.
"It is a test for the Brazilian political system. Its credibility is at stake," said David Fischer, a political scientist at Brasilia University.
Those implicated include Lula's ex-chief of staff Jose Dirceu, ex-communications minister Luiz Gushiken, and ex-transportation minister Anderson Adauto, as well as nearly a dozen ex-legislators in the governing coalition.
Prosecutors believe that Dirceu, a 66 year-old lawyer, former PT leader and Lula's political enforcer during his first term in office, was the mastermind behind the corruption network.
If found guilty, he faces at least 15 years prison.
According to the opposition Brazilian Social Democratic Party (PSDB), up to $50m was doled out in bribes.
However a lawyer for Dirceu insists there were no Mensalao payments.
"There was no so-called vote-buying," the lawyer, Jose Luiz Oliveira Lima, told the daily O Globo Wednesday.
"There is no proof of any use of public money. Dozens of witnesses categorically say that Dirceu had no knowledge of the loans and [money] transfers," he said.
Attorney General Roberto Gurgel earlier called the case "the most daring and outrageous corruption scheme and embezzlement of public funds ever seen in Brazil".
The trial, which has received blanket coverage in the Brazilian media, is expected to last for a month and could affect the outcome of municipal elections in October that will set the political map for the 2014 presidential vote.
Defence arguments begin on Friday.
This is Brazil's highest-profile corruption scandal since president Fernando Collor de Melo resigned in 1992 after serving half of his four-year term in office. A Senate trial found him guilty of corruption and barred him from public office for eight years.