Twelve of the 25 people convicted in Brazil's biggest-ever corruption case will get new trials, the Supreme Court ruled Wednesday.

The case deals with a congressional vote-buying scheme that operated during the first two years of President Luiz Inacio Lula da Silva's 2003-2011 tenure.

The dean of the 11-member court, Celso de Mello, joined five of his colleagues in accepting defense motions for new trials.

Because the case originated with the Supreme Court, that tribunal is obliged to re-hear the cases of those defendants whose convictions were approved with the votes of only seven justices, De Mello said.

The 12 defendants granted new trials included the highest-profile figures in the case, such as Lula's chief of staff, Jose Dirceu.

"The protection of prisoners' rights is a constitutional duty from which the Supreme (court) cannot exempt itself, even against popular clamor," De Mello said, alluding to widespread public demands that all 25 defendants be jailed immediately.

Some legal experts say the grant of new trials could extend the case into 2016, at which point the statute of limitations would become a factor.

Dirceu spent two decades as the political right arm of Lula, founder of the Workers Party, or PT, which remains in power under President Dilma Rousseff.

Once seen as the natural heir to Lula, Dirceu was forced to resign as presidential chief of staff in the summer of 2005 after lawmaker Roberto Jefferson accused the PT of having bribed legislators of other parties to build the congressional majority that the government failed to obtain at the polls in 2002.

The scandal didn't stop Lula from winning a second four-year term in 2006 or from helping his anointed successor, Rousseff, to prevail in the 2010 presidential contest. EFE