The court's second chamber on Tuesday agreed to rule on two petitions for the release of former President Luiz Inacio Lula da Silva (in office between 2003-10): one for alleged irregularities during the trial and the other for suspicions against ex-judge Sergio Moro, who found Lula guilty of corruption and was later offered the justice portfolio by current far-right President Jair Bolsonaro.
The first petition was an appeal against a Supreme Court ruling rejecting the release of the ex-leader in mid-2018.
According to four of the five judges, the decision taken at the time by the Supreme Court did not, as Lula's defense team had argued, violate the country's legal framework, reported Efe news.
However, the judges still had to decide on another habeas corpus submitted by the defense of the former President requesting a review of the trial on suspicion that Moro had behaved in a way that was biased and outside the rule of law.
This second appeal began to be heard late last year but the session was suspended as Gilmar Mendes - one of the judges - requested more time to analyze the details of the case.
By that time, judges Carmen Lucia Antunes and Edson Fachin had already ruled to deny Lula the habeas corpus, but when the hearing was resumed on Tuesday, Mendes voted in favour of the appeal.
Judge Ricardo Lewandowski agreed with Mendes and also voted for the appeal, but the last judge to vote, Celso de Melo, joined those rejecting the defense's petition and the decision to keep Lula in prison came down to a narrow 3-2 vote on the five-magistrate panel.
The judges also postponed until the second half of the year the debate on the conduct of Moro, the federal judge-turned-minister who handed down Lula's prison sentence.
Public controversy over the way Moro conducted the trial against Lula lit up in recent weeks following the release of messages the former judge allegedly exchanged during the trial with prosecutors of the anti-corruption Lava Jato ("Car Wash") operation, which led the ex-President to be jailed.
Nonetheless, the second chamber heard an earlier appeal that accused Moro of bias and said that this claim was substantiated last year with the appointment of the former judge as a minister in Bolsonaro's government.
Bolsonaro is the leader of the far-right Social Liberal Party and was considered the main political opponent of Lula, a progressive former trade unionist.
The messages complicating the case were exchanged via the encrypted messaging service Telegram during the trial against Lula and may suggest that Moro, in some way, directed the prosecutors' work, something expressly prohibited by law.
Moro has vehemently denied the authenticity of those messages, which were leaked to the website The Intercept by a hacker, and has asserted that his conduct as a judge was above reproach.
( With inputs from IANS )