(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.

Assassination of Rights Defender & Driver in Brazil

Prompt investigation needed into killing of councilwoman @mariellefranco & Anderson Gomes.

Marielle advocated for victims of police abusehttps://t.co/9POtrfUUnG Photo by Mídia Ninja pic.twitter.com/C80Q9hRTd3 — Human Rights Watch (@hrw) March 15, 2018

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.

Read More