BRASILIA (Reuters) - The Supreme Court decided on Monday to return a corruption investigation into former Brazilian President Luiz Inacio Lula da Silva to a crusading anti-corruption judge who is presiding over cases in the sprawling Petrobras graft scandal.


Lula, Brazil's most influential politician, who has not ruled out running again in 2018, is under investigation for allegedly benefiting, in the form of payments and a luxury apartment, from the corruption scheme uncovered at the state-run oil company.


The Supreme Court took over the Lula investigation from lower court judge Sergio Moro in March after he released a wiretap of a conversation between Lula and then-President Dilma Rousseff as evidence she was appointing him to her Cabinet to shield him from prosecution.


But on Monday, Supreme Court Justice Teori Zavascki ruled the recording was inadmissible as evidence because it was taped after the warrant expired and he sent the Lula case back to Moro, exposing Lula to possible arrest and prosecution.


If Lula is convicted of any crime, he could not run for president for eight years under Brazil's clean-slate law.


Rousseff, his successor and protégée, was suspended last month when the Senate voted to put her on trial for breaking budget laws, ousting Lula's Workers' Party after 13 years in power. The impeachment trial is expected to conclude in August. If she is convicted, interim President Michel Temer, of the PMDB party, will serve out her term through 2018.

Brazil's largest-ever corruption investigation has uncovered a massive graft scheme in which local construction and engineering firms colluded to overcharge Petrobras for work and used the excess funds to bribe executives and provide kickbacks to politicians in Rousseff's governing coalition.

Elected politicians can only be tried by the Supreme Court. To date, only one has been put on trial there, the suspended speaker of the lower house of Congress, Eduardo Cunha, who is facing several investigations into millions of dollars in bribes and undeclared bank accounts in Switzerland.

A congressional ethics committee will vote on Tuesday on whether to strip Cunha of his seat and his relative immunity as a lawmaker for lying to the chamber about his Swiss accounts.

Prosecutors in the Petrobras investigation filed a civil lawsuit against Cunha and his wife on Monday seeking the return to public coffers of $5.7 million in graft money. They called for Cunha to be stripped of his political rights for 10 years.

(Reporting by Anthony Boadle; Editing by Peter Cooney)