Residents watch youth groups gather for a crimes against young people march in the slums of Medellin, Colombia, on Tuesday March 29. The peaceful demonstration was organized in response to the shooting death of 17-year-old rapper Mario Alejandro Sierra on Saturday. Since January, 340 people have been killed in Medellín - a city of just over two million inhabitants - said Yesid Henao, deputy secretary of the youth services department.