For some, seeing Brazil’s most commanding political figure in jail was the culmination of the anti-corruption drive and evidence that the law was finally being applied equally to everyone. For others, it was evidence that the investigation was politically contaminated and beginning to backslide into the influence trading it was intended to remedy.

The unusual zeal and speed with which the leftist firebrand’s case was handled made it politically fraught: When Mr. da Silva was imprisoned in April of last year to start serving a 12-year sentence for corruption and money laundering, he was the front-runner in the presidential race. The conviction blocked him from the ballot and paved the way for the election of the far-right candidate Jair Bolsonaro.

Suspicion that the prosecution was politically motivated only grew after Sérgio Moro, the judge who handled Mr. da Silva’s case, joined President Bolsonaro’s cabinet as justice minister. That appointment — which came with a promise of an eventual seat on the Supreme Court — outraged politicians on the left and tarnished the image of Mr. Moro, who had become a folk hero at home and a celebrated jurist abroad.

“If there’s one thing a judge needs, that is autonomy from the political establishment,” said Margarita Stolbizer, a former lawmaker in Argentina and prominent activist against graft who said she was astonished by Mr. Moro’s decision to join Mr. Bolsonaro’s cabinet. “I felt he defrauded us, considering the image he sold of himself.”

Mr. Moro declined a request for an interview. In response to emailed questions, some of which he did not answer, he said he saw the cabinet post as an opportunity to “consolidate the advances that have been made on anti-corruption and extend them to the fight against organized crime and violent crimes.”

Mr. Moro’s legacy suffered a further blow when The Intercept Brasil, an online news outlet, began reporting in June on a trove of leaked text messages exchanged by federal prosecutors. The messages showed that Mr. Moro had provided guidance to the prosecution in Mr. da Silva’s case.