State prosecutor Jorge Gonzalez yesterday said that the three masked men pulled up in a car and then shot Marisela Escobedo Ortiz.
Their victim had been protesting for three days in front of the governor's palace in Chihuahua. She had been campaigning for justice in the killing of her teenage daughter since a judge exonerated the main suspect in April.
The body of Rubi Frayre Escobedo, 17, was found dismembered and burned in 2008. Her live-in boyfriend had been charged with her murder.