Three days of mourning have begun in Rio de Janeiro, Brazil, after the murder of a black human rights campaigner who spoke out against the lethal methods routinely used by security forces within the city's poorest neighborhoods.Many residents of Rio are hardened to daily incidents of deadly violence yet the killing of Marielle Franco, a city council member and civil society activist, is being met by a huge wave of anger and indignation on social media, and protests on the streets.Flowers, pictures and condolence messages are amassing outside the city council offices, paying tribute to a charismatic young woman with a long record of championing social causes in a metropolis plagued by issues of violence, race and poverty.A crowd of several thousand gathered there Thursday, brandishing slogans alleging that Franco was executed, and demanding that Rio's military police be disbanded. "How many more have to die?" asked one.Investigators reportedly suspect that Franco, 38, was the victim of a targeted assassination. She was shot at around 9:30 p.m. Thursday in Estacio, a downtown neighbourhood, as she was returning from an event about empowering black women in Brazil, a cause she passionately championed.Reports say two men in a car drew up alongside her vehicle, opened fire, and sped away. Her driver, Anderson Pedro Gomes, was also killed, and an aide was injured.The outcry over Franco's death comes a month after Brazil's president, Michel Temer, signed a decree placing the military in overall charge of security in the state of Rio de Janeiro. His government portrayed this as an attempt to curb rising violence, particularly in favelas, between drug gangs and the police.Last year, 6,731 civilians were killed statewide, according to Rio's Institute of Public Security. This year, the figure in one month alone — January — was 649, including 154 killed by police during various operations.The deployment of Brazil's military — which security analysts say has so far failed to make any obvious difference — was strongly criticized by Franco who feared this would lead to still more bloodshed and human rights abuses. Franco was born in a giant Rio favela — or shantytown — and was a powerful critic of Rio's military police and their tactics within these neighborhoods. Last week, she spoke out after the police shot two youngsters in Acari, a neighborhood in the northern part of Rio.One of her last posts on Twitter highlighted the shooting death of a young man, describing this as "another homicide...that could be credited to the police." In a previous message, she labeled a military police unit as "the battalion of death" because of the number of civilians shot by its officers.Franco was considered to have a promising political future in a country that has become deeply cynical about its established leaders and parties after a series of huge corruption scandals. A member of a small leftist group, she was believed to be contemplating running for election to Brazil's Congress."She was becoming a very relevant, significant leader herself, of the feminist and anti-racism movements, and movements against inequality.Those were her issues," said Luiz Eduardo Soares, a former public security secretary with Brazil's federal government, and co-author of Elite da Tropa, a book about Rio's military police.He added: "She was really beautiful and charismatic, so this is really shocking for everyone who knew her and followed her."State and federal law enforcement agencies have announced investigations into the killing of Franco. Civil Police chief, Rivaldo Barbosa, told a meeting of security officials that "we will respond in a manner befitting this most grave crime." He said no possible motive is being ruled out. Copyright 2018 NPR. To see more, visit http://www.npr.org/.