Brazilian councilwoman Marielle Franco was shot dead in an assassination-style killing on Wednesday night.

Franco was shot several times as bullets sprayed her car as it drove through Rio de Janeiro's dangerous north side. Her driver was also killed, while her press officer survived the attack.

Officials said the 38-year-old leftist lawmaker was likely targeted for her outspoken criticism of police brutality and killing of innocent people in Rio de Janeiro's violent slums.

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"It is far too soon to say, but we are obviously looking at this as a murder in response to her political work, that is a main theory," a Rio de Janeiro public prosecutor told the Reuters news agency on condition of anonymity.

Authorities investigate the scene of Marielle Franco's killing

Another police official said that the killers must have known exactly where she was sitting in a car that had tinted windows.

In a statement, Brazil President Michel Temer described Franco's killing as "an attack on democracy and the rule of law." Raul Jungmann, the minister of the newly established Public Security Ministry, said that federal police forces would help investigate her death.

Franco calls out Rio police brutality

Just a day before her death, Franco blamed police for the killing of a young man in a favela. "Another killing of a young man that could be chalked up to the police. Matheus Melo was leaving church when he was killed. How many more will have to die for this war to end?" she posted on Twitter.

A few days earlier, she accused a local police unit in the poor neighborhood of Acari of acting like a death squad. "They come to carve up the population! They come to kill our young!" she tweeted.

The reported rise in police violence comes on the back of a federal government decree that allows the army to take over all security operations in Rio until the end of the year. The measure has seen generals take charge of almost all local security branches, while heavily armed soldiers are routinely deployed to accompany police officers during sweeps and searches in favelas.

International bodies and rights group condemn killing

In a statement on Thursday, Liz Throssell, the spokesman for the United Nation's Human Rights Office, welcomed the investigation into Franco's death, but also stressed that any probe "must be thorough, transparent and independent if it is to be seen as credible."

Amnesty International's Brazil director, Jurema Werneck, said that Franco's murder was "yet another example of the dangers that human rights defenders face in Brazil," adding that the Brazilian government "cannot stand by and let human rights defenders be killed with impunity.”

A product of Rio's slums

Franco was raised and lived in a complex of slums called Mare. The network of favelas is known for being one of Rio's most dangerous areas. The area's 130,000 residents are forced to contend with the presence of the city's two largest gangs, the Red Command and the Pure Third Command, as well as several militias made up of off duty and retired police officers and firemen.

Franco was elected onto the city's council in 2016 on a campaign that focused on police violence and the rights of women of women and people of African descent. She received some 46,500 votes, a total only bested by four of the council's 51 elected representatives.

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Vigils and protests were planned across at least seven major Brazilian cities on Thursday, while members from her Socialism and Liberty Party (PSOL) carried flowers into Brazil's federal Congress, along with several signs demanding justice.

By Thursday morning, around 1,000 people had gathered in central Rio to mourn Franco's death, while some 30,000 more had signaled their intention on social media to attend at least one of several rallies later in the day.

Some 30,000 people said they intend to take to the streets to mourn slain lawmaker Marielle Franco

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dm/kms (Reuters, AP, AFP, dpa)