Lawyers for Chiquinho Brazão, who served on Rio’s council at the same time as Franco and is now a congressman, and former police chief Rivaldo Barbosa, said their clients denied any wrongdoing, according to local media.

Brazil’s Justice Minister Ricardo Lewandowski said in a press conference that the motivation for the crime is “complex because that group [the Brazãos] has multiple interests”.

He said investigations have suggested lawmaker Chiquinho Brazão was especially upset about a bill that his then-colleague Franco sponsored at the city council about regulation of land to build public housing in Rio.

“At this moment we have it very clear who are the perpetrators of this hateful, heinous crime of political nature,” said the minister, who added that four other people had documents seized. Among them, he said, is a police detective who also investigated the case, Giniton Lages. Lewandowski also said the men jailed earlier will be transferred from Rio to the capital Brasilia.

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The arrests of the men who allegedly ordered Franco’s killing came four days after Brazil’s Supreme Court validated a plea bargain for the shooter, who was arrested along with the driver in 2019.

The investigation into Franco’s murder had been troubled for years. Rio’s state civil police could not break the case after the arrest and indictment of the shooter and the driver. The lead detectives were changed four times before February 2023. Federal authorities then attempted to take control of the case, but were not allowed to, which also increased suspicions of obstruction, according to Lewandowski.

The driver admitted to the double murder of Franco and her driver. The shooter, disgraced former police officer Ronnie Lessa, signed a plea bargain deal with authorities in January and his admission led to Sunday’s arrests.

Barbosa, the head of Rio’s police when the murder took place, was also arrested for alleged obstruction of the investigation, federal police chief Andrei Rodrigues said in a press conference.

“He actively sought to detour the investigation from those who ordered the killing,” Rodrigues said. Earlier, Franco’s widow Monica Benicio said Barbosa offered her his sympathies after her wife was slain, promising to be tough in his efforts to find the killers.

Franco worked as an assistant to then-state lawmaker Marcelo Freixo in 2008, as he presided over a special committee investigating militias in Rio’s state assembly. Freixo’s final report indicted 226 suspected militia members and politicians and government employees, including Domingos Brazão. While Brazão was mentioned in the report, he was not indicted.

Political violence is not uncommon in Rio, and such killings are often linked to territorial and political disputes. But they typically go unsolved and never elicit the same level of outcry as Franco’s death did. She had been a rising political star, making her name by exposing police abuse and violence against residents of working-class neighbourhoods known as favelas.

Known universally by her first name, Franco grew up in a favela herself – the Mare neighbourhood near Rio’s international airport. She became a human-rights activist there after her friend was killed by a stray bullet in a shoot-out between police and drug traffickers. She worked for Freixo investigating organised crime then went on to win a seat on Rio’s city council in 2016. She kept receiving and sharing complaints of police abuse until just days before she was killed.

She stood out as one of the only black women on the council and, while her assertiveness and mere presence ruffled some, she remained unbowed.

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On the evening of March 14, 2018, Franco left an event to empower young black women when a car pulled up alongside hers and opened fire. Franco and her driver, Anderson Gomes, were killed on the spot.

“Why did they choose Marielle? No doubt it was because she is a black woman, they were sure they would go unpunished,” Freixo said on X, formerly Twitter. He wrote that crowds gathered a day after her murder to mourn her and those who killed her were not able to see “the greatness of what Marielle stood for”.

The brutality of Franco’s murder and the political hope she had embodied transformed her into a symbol of left-wing resistance in Brazil and abroad. People staged massive protests to channel their outrage; her silhouette was painted on walls across Brazil and printed on T-shirts; her name figures on a street sign in front of Rio’s city council; and her sister, Anielle Franco, has been appointed Brazil’s minister of racial equality.

The Brazão brothers’ political clan is associated with an area of the city historically dominated by militias – groups initially made up mainly of former policemen and off-duty officers who wanted to combat lawlessness in their neighbourhoods with armed force.

They began to extort shop owners and charge for services such as internet, cooking gas and cable television. More recently, they have expanded their illicit businesses into land grabbing and property development.

Brazil’s lower house will vote sometime soon whether its lawmaker Chiquinho Brazão’s arrest will stand. A simple majority of 257 votes could set him free as investigations move forward. A staunch supporter of former president Jair Bolsonaro, Brazão is likely to count on meaningful support from his peers.