RIO DE JANEIRO — On the eve of her killing on a downtown street on Wednesday night, a Rio de Janeiro councilwoman suggested that the death of a young man earlier in the week had been the latest act of police brutality.

“How many more must die for this war to end?” Councilwoman Marielle Franco wrote on Twitter.

The death of the young man, Matheus Melo, 23, received modest news coverage. He was, after all, a poor black man in a city where scores of poor black men are killed each year. Many die at the hands of the police, without much, if any, consequence.

Ms. Franco’s killing shattered the cavalier attitude that prevails in much of this megacity in the face of rising violence.

Shortly after 9 p.m. as the councilwoman was heading home from a meeting about empowering black women, assailants sprayed her car with bullets. They killed the 38-year-old rising political star and her driver, Anderson Pedro Gomes.