Brazil's Supreme Court convicted three top aides of former president Luiz Inacio Lula da Silva of graft related to a vote-buying scheme in Congress.
Lula's ex-chief of staff Jose Dirceu was found guilty by six of the 10 judges in connection with the scheme that ran from 2002 to 2005 during the popular president's first term, a court spokesman said.
The head of Lula's ruling Workers' Party (PT) at the time, former guerrilla Jose Genoino, and its treasurer, Delubio Soares, were also convicted on charges of corruption.
The three officials are among 37 former ministers, lawmakers, businessmen and bankers on trial before the Supreme Court over the scandal known as "Mensalao" (big monthly payments).
Since the trial opened in early August, 30 of the defendants have already been found guilty.
The justices said Dirceu, Genoino and Soares distributed money to lawmakers to "illegally secure the support of other political parties to form a ruling government coalition."
Buying political support in Congress is a common practice in Brazil and the defense insisted said that the illegal account was used only to cover campaign costs.
The 66-year-old Dirceu, who operated as Lula's de facto prime minister, is viewed as the main culprit in the high-profile trial that threatens to tarnish the ex-president's legacy.
The scandal nearly cost Lula his re-election in 2006. But the 66-year-old founder and leader of the leftist PT was cleared.
Lula was easily re-elected in 2006 and handed over power to his protegee and fellow PT member Dilma Rousseff at the end of his second four-year term.
Dirceu's rise began in 1995, when the lawyer, economist and ex-communist assumed the PT presidency.
He had been arrested during a student congress in 1968 before being released a year later along with a group of political prisoners exchanged for the US ambassador to Brazil at the time, Charles Elbrick, who had been kidnapped by leftists.
Dirceu later traveled to Cuba, where he underwent guerrilla training, although he has always maintained he never took part in the armed struggle.
Earlier this month, Supreme Court Justice Joaquim Barbosa said that evidence showed Dirceu "masterminded the operations" of Soares, the treasurer, and businessman Marcos Valerio.
Prosecutors alleged the bribe money was skimmed from advertising budgets of state-owned companies through a company owned by Valerio, also among the accused.
Dirceu was forced to resign in 2005 when the graft scandal came to light. But Lula's top lieutenant has always denied paying bribes to lawmakers.
The convictions were announced in between the two rounds of nationwide municipal elections.
But despite the blanket media coverage of the trial, the PT did not appear to have been hurt in Sunday's first round.
Rousseff's party did not do so well in some major cities, but it improved its gains by 14 percent nationwide compared with the 2008 municipal polls and Brazil's first female president enjoys a 77 percent approval rating.
"The conviction of Dirceu and Genoino has a very strong symbolic effect in Brazil where, as in other young democracies, there is a perception of impunity, particularly with respect to politicians," said political analyst Rafael Cortez of the Tendencias consulting firm.
None of the accused, who face charges ranging from embezzlement and money laundering to corruption and fraud, have been arrested, and none are in court.
The sentences will not be announced until the end of the trial, which could run for several more weeks.
Lula, who is recovering from throat cancer, has insisted he was betrayed and offered public apologies on behalf of his party.
The trial marks the most significant corruption case in Brazil 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.