Judge Moro and Brazilian prosecutors believe that a deeper political transformation can be achieved only through sweeping changes like overhauling campaign finance rules, doing away with the de facto immunity members of Congress enjoy in office and winnowing down the vast number of political parties, to curb horse trading.
None of these changes is on the table. President Michel Temer, who was charged in June with ordering a bribe to silence a jailed politician, and other powerful politicians under criminal investigation are lashing out against the judiciary. Mr. Temer recently asked the Supreme Court to bar Attorney General Rodrigo Janot from taking further legal action against him, accusing him of a baseless crusade.
Members of Congress have introduced legislation that would make it easier to rein in judges who, the politicians contend, are abusing their authority by ordering pretrial detentions and relying too heavily on plea deals.
“Brazil is at a tipping point and it’s unclear right now which of these two forces is going to be victorious,” said Matthew Taylor, an expert on Brazil’s judicial system at American University.
Judge Moro, a studious, sullen lawyer who spent the early years of his career studying the history of money laundering and corruption investigations, is widely credited with setting up that clash.
In 2004, when he was still a relatively unknown judge in this city settled by German and Italian immigrants, he published an article in a legal journal about the factors that enabled Italy’s far-reaching “Clean Hands” corruption investigation. The use of pretrial detentions, plea agreements and the ability to shape news coverage enabled Italian law enforcement officials to create a “virtuous cycle” that led to the downfall of scores of powerful political figures, Judge Moro concluded.
It took a decade and a “highly improbable set of necessary conditions,” said Deltan Dallagnol, a Lava Jato prosecutor, for Brazil’s judiciary to start applying the tactics of “Clean Hands.”
It began in early 2014 with a routine investigation into money laundering at a gas station in Brasília, which eventually led investigators to unravel a gargantuan web of kickbacks at Petrobras.
Critical cases in the inquiry were assigned to a close-knit team of federal police officers and prosecutors in Curitiba that happened to have expertise in financial crimes. A new electronic case system allowed judges to expedite cases that had lagged for years. Switzerland, long a haven for stolen public funds, agreed to share information with Brazilian prosecutors. A 2013 update to Brazil’s penal code made it easier to turn defendants into cooperating witnesses by offering them leniency.
And then there was Judge Moro.
In May 2014, he startled the legal community by demanding that a former Petrobras chief, Paulo Roberto Costa, be held pending trial, calling him a flight risk. In doing so, he stared down a Supreme Court judge who had signed off on Mr. Costa’s release. But Judge Moro prevailed, and with Mr. Costa behind bars, several other suspects agreed to cooperate with investigators.
As a cascade of new charges were filed against politicians and Petrobras executives, Judge Moro soon became a celebrity. During a visit to a supermarket in Curitiba, an employee took to the loudspeaker to announce his presence. At large protests in 2015 against the government of President Dilma Rousseff, previously the chairwoman of Petrobras, many demonstrators wore Moro masks and T-shirts with the slogan “We are all Sérgio Moro.”
Many Brazilians hoped the judge would run for office, a prospect he has ruled out. Judge Moro, who comes across as reserved and taciturn, said that he stumbled into the limelight but that his newfound fame had served the investigation well.
“It was important so that these cases, which implicated powerful people, weren’t obstructed in some way,” he said.
As the cases advanced, Judge Moro and the Lava Jato prosecutors began to make a broader argument to the public about the need to change the nation’s political culture.
In March 2016, he issued a public statement praising anti-corruption protests, denouncing “the systemic corruption that destroys our democracy, our economic well being and our dignity as a nation.” Last October, as he sentenced a former senator to 19 years in prison, Judge Moro quoted a 1903 speech by President Theodore Roosevelt in his ruling.
“The exposure and punishment of public corruption is an honor to the nation, not a disgrace,” the quoted portion said.
Perhaps Judge Moro’s most contentious move also came in March 2016, when he released the transcript of an intercepted conversation between Mr. da Silva and his successor, Ms. Rousseff. In it, she appeared to offer a cabinet position to Mr. da Silva, which would have shielded him from prosecution in conventional courts.
The revelation fueled public outrage that contributed to Ms. Rousseff’s ouster last year. But it also focused anger on Judge Moro. Even some legal experts who support his work have argued that releasing the wiretap was improper because the warrant used to record the call appeared to have expired when the conversation took place. The judge says he has no regrets.
“I think that democracy wins when, shall we say, people learn what their leaders do in the shadows,” he said. “Especially when what they’re doing is illicit.”
Prosecutors charged Mr. da Silva in 2015 with corruption, accusing him of illegally receiving about $1.1 million in improvements and expenses for a beachfront apartment. They have also described him as the mastermind of the kickbacks scheme at Petrobras. As the case unfolded, the Brazilian news media covered it as a duel between two titans — Judge Moro and the leftist former president — that could shape the broader political future of Brazil.
Last month, in finding Mr. da Silva guilty, Judge Moro wrote that “no matter how important you are, no one is above the law.” The decision has thrown into turmoil next year’s presidential election, in which Mr. da Silva is currently the front-runner. He could be barred from running.
With the appeal pending, Mr. da Silva’s supporters are attacking Judge Moro and the Lava Jato team. This month, supporters held a mock trial in Curitiba, accusing them of abusing pretrial detentions, offering questionable plea bargains and trying the case in the press.
“Judge Moro cannot continue behaving like he was a czar,” Mr. da Silva said late last month in a radio interview.