Grigoropoulos , Monday , was killed by a police bullet in 15 . Demonstrators clash with police October even before the official march begins . A police officer was found guilty in 15 of culpable homicide .
Alexis Grigoropoulos , 15 , was killed by a police bullet in December 2008 . Demonstrators clash with police Monday even before the official march begins . A police officer was found guilty in October of culpable homicide .