A petrol bomb thrown by protesters explodes in front of policemen during clashes, following a rally commemorating the killing of a 15-year old student back in 2008, in Athens, on Sunday, Dec. 6, 2015. Hundreds of protesters marched through the streets of the Greek capital to mark the seventh anniversary of a fatal police shooting of the teenager. Fifteen-year-old Alexis Grigoropoulos was killed on the night of Dec. 6, 2008, when a policeman fired his gun following an argument in the center of Athens. (AP Photo/ Yorgos Karahalis ), APTOPIX