Thousands demonstrated in Rio Thursday after the killings of Marielle Franco and her driver.
CNN  — 

Thousands of angry and distraught Brazilians have taken to the streets to protest and mourn the shooting death of Marielle Franco, a Rio de Janeiro councilwoman and a prominent critic of police killings in shantytowns.

Franco and her driver Anderson Pedro Gomes were killed Wednesday night in Rio’s Estacio neighborhood when a car pulled up beside them and someone inside shot at them. A press secretary who worked for Franco was sitting the back seat and was injured.

Political violence is not an uncommon phenomenon in Brazil. It usually erupts in smaller and more impoverished cities.

In Rio, violence has risen and weeks ago, the federal government decreed that Brazil’s army would take over all security operations through the end of the year to tackle that problem.

Franco slammed the federal government’s move, saying it could aggravate police violence against residents. She had been appointed rapporteur for a special commission to monitor the federal intervention.

Widespread outrage

Brazilian President Michael Temer called the killings a “cowardly attack” and called for an investigation. Human rights activists also denounced the deaths of Franco and her driver.

Marchers took to the streets in Rio, Sao Paulo and other cities.

Demonstrators rally in Sao Paulo after the killings.

At Rio’s City Council building, Franco’s body briefly lay in state. More vigils and protests are being planned.

The United Nations office in Brazil, as well as Amnesty International and Human Rights Watch, called for a timely and transparent probe into the murders.

The hashtag #JustiçaParaMarielle has been trending on Twitter.

‘Outspoken and courageous’

Franco, 38, was born and raised in the poor neighborhood of Complexo da Mare and was elected to the city council two years ago. Along with fighting violence by police, she advocated rights for women and people of African heritage.

“Marielle was an outspoken and courageous advocate for victims of police abuse and a tireless defender of the rights of women and Afro-Brazilians,” said Maria Laura Canineu, Brazil director at Human Rights Watch.

She said Franco and her driver “are the latest victims of a security system that has long failed to stop violence, or to ensure justice for the victims.”

“The climate of near total impunity in Rio de Janeiro needs to end once and for all,” Canineu said.

Human Rights Watch said in the days before her killing, Franco tweeted about police killings in Rio.

Jurema Werneck, Amnesty International’s Brazil director, called the deaths “a chilling development” and an example of the perils experienced by human rights activists.

“As a member of Rio de Janeiro’s State Human Rights Commission, Marielle worked tirelessly to defend the rights of black women and young people in the favelas and other marginalized communities,” Werneck said.

CNN’s Roba Alhenawi and Natalie Gallon contributed to this report.