Police and demonstrators have clashed in the Greek capital, after thousands of people gathered to mark the anniversary of a police shooting. The demonstration marks two years since police shot dead 15-year-old Alexandros Grigoropoulos. His death sparked weeks of rioting, the worst Greece had witnessed in several decades, bringing the capital to a standstill. Last October, a police officer was jailed for life and another for ten years over the shooting. Al Jazeera's Nadim Baba reports from Athens.