What does the demonstration protest against?

Greek police have used tear gas against protesters throwing stones. Thousands of demonstrators have gathered on the first anniversary of the police killing of a 15-year-old boy. The protesters broke windows of businesses and threw firecrackers and other objects at the police. Officials say about 50 people have been arrested. Greek media say an administrator at Athens University was taken to a hospital after being attacked by protesters who entered the university offices. The two police officers involved in last year’s shooting said they had fired warning shots. But witnesses said one of the officers aimed at the boy.