A leading figure from the government of former Brazilian president Luiz Inacio Lula da Silva played a central role in a major corruption scheme, a court has heard.
Judges at the Supreme Court have begun delivering their findings on Jose Dirceu, Lula's chief of staff from 2003 until 2005.
Mr Dirceu used public funds to pay opposition parties for support in Congress, Judge Joaquim Barbosa said.
Mr Dirceu denies any wrongdoing.
The case, with 37 defendants, is seen as a key test of Brazil's ability to hold its politicians to account for corruption.
Judge Barbosa, who is the rapporteur of the case, also found seven other key figures in Lula's Workers Party guilty of corruption.
Among them are former party president Jose Genoino and former party treasurer Delubio Soares.
Evidence presented in court showed that Mr Dirceu "organised and led a criminal operation", Judge Barbosa said.
The scheme used public funds to make "illegal payments and other benefits" for congressmen who agreed to support the government in crucial votes, he added.
Some of the defendants, who include politicians and business executives, say the scandal is being exploited by opposition politicians and sections of the media.
They say that the scheme, dubbed the "Mensalao" or "big monthly payment", was simply a way of paying off campaign debts which, while illegal, is common in Brazilian politics.
Others deny any involvement in buying political support.
Other Supreme Court judges still need to present their findings, which may push a verdict until next week.
A majority of the judges has already rejected claims by the defence that no vote-buying scheme existed.
To date, 22 of the 37 defendants have been convicted of allegations ranging from corruption to money-laundering. Four have been acquitted.
The case, which began two months ago, has been called the trial of the century in Brazil.
The Mensalao scandal almost led to the downfall of Lula's government in 2005, but he was comfortably re-elected the following year.
The allegations have taken several years to get to court.
Lula is not directly implicated in the case and has denied any knowledge of the scheme.
He left office with huge approval ratings, and remains a popular figure in Brazilian political life.
However, analysts say a series of guilty verdicts may tarnish his reputation.
The case reaches a decisive moment just ahead of important local elections on Sunday.
Among the most important posts to be decided in a tightly contested race is for the mayor of Sao Paulo, Brazil's biggest city.