Friends and relatives of the murdered Brazilian politician Marielle Franco are demanding answers after Adriano da Nóbrega – a notorious hitman, whose gang of contract killers is suspected of involvement in her assassination – was gunned down by police in the north-east of the country.

Nóbrega, an ex-special forces police captain, also had close links to the family of the far-right president, Jair Bolsonaro. Nóbrega was killed by police on Sunday in Bahia state where he had been on the run.

“Who gained from the death of ex-special forces captain Adriano Nóbrega,” tweeted Franco’s widow, Monica Benicio.

Franco’s leftist PSOL party said Nóbrega was a “key piece” in discovering who ordered Franco’s killing and called for a full investigation. “Witness elimination? Another attempt at obstruction of justice? Who ordered our companion killed? We demand answers,” tweeted Sâmia Bonfim, a PSOL congresswoman.

Police insisted that was not the case, claiming Nóbrega had opened fire on officers when they attempted to apprehend him in Esplanada – a small town 1,700km north of Rio.

Maurício Teles Barbosa, the security chief in Bahia state, said: “We attempted to carry out the arrest but the target preferred to respond by shooting.”

Nóbrega was hiding in a country property owned by a local councillor for the PSL party for which Bolsonaro was elected, but has since left. Gilsinho de Dedé told the G1 news site he had no idea Nóbrega was hiding there, had never met him, and suspected the fugitive had broken in.

Franco was killed in March 2018 and paramilitary gangs – mafias made up of serving and former police officers who control vast swathes of Rio state – are widely believed to have been involved in her murder.

Two former police officers are imprisoned, accused of killing her but deny the accusations. The suspected shooter, Ronny Lessa, lived in the same Rio condominium as Bolsonaro and his son Carlos – both have denied the accusations. Lessa had allegedly been a member of Nóbrega’s gang, called the Crime Bureau. As well as contract killings, it ran construction rackets in west Rio.

“The question we have to ask is: in whose interest does it serve that Adriano has been killed?” said José Alves, a professor of social science at the Federal Rural University of Rio de Janeiro who has studied the state’s paramilitary gangs. “He could have taken the investigation of the death of Marielle to a new level.”

Marcelo Friexo, a leftist congressman who was very close to Franco, said: “Adriano was a very violent person and it is possible he did not want to give himself up alive, just as it is also possible he was executed… He had a lot of involvement with the Bolsonaro family.”

Nóbrega, his wife and his mother are named in a criminal investigation into allegations of embezzlement, money laundering and racketeering involving Bolsonaro’s son Flávio, ex-police officer Fabrício Queiroz and others. Nóbrega and Queiroz had previously served in the same police battalion.

Prosecutors believe that Queiroz collected some of the salaries of staff employed in Flávio Bolsonaro’s cabinet when he was a representative at Rio’s state legislature and paid the money back to him which he laundered through a chocolate shop and properties.

Flávio Bolsonaro and Queiroz have denied the allegations. “I always did everything correctly within the law,” Flávio said in December, arguing he is being persecuted. In written testimony last year, Queiroz said he chose cabinet aides and “managed” their salaries to “intensify political performance” without telling his superiors, the O Globo newspaper reported.

Nóbrega’s wife, Danielle Costa, and mother, Raimunda Magalhães, were both employed in Flávio Bolsonaro’s office. Prosecutors described them as “‘ghost employees’… who transferred resources back to the operator Fabrício Queiroz.” Nóbrega “was also benefited by some of the resources,” prosecutors said in court documents seen by the Guardian.

In December a Rio court authorised searches of properties – including the chocolate shop. But this month, a separate investigation by federal police concluded there was no evidence of money laundering in Flávio Bolsonaro’s property deals.

As a state deputy, the president’s son was instrumental in Nóbrega being given a medal by the assembly while he was imprisoned under suspicion of homicide. Nóbrega was later cleared.