Grigoropoulos's death in 2008 in an altercation with police during a night out sparked violent riots across the country lasting almost a month during which public buildings and cars were set aflame while shops were looted and barricades erected.
Demonstrators in Greece threw firebombs and pelted police with rocks Thursday as marches on the 10th anniversary of the fatal police shooting of a teenager degenerated into violence.
Clashes also broke out during demonstrations in the northern city of Thessaloniki, with police firing tear gas and stun grenades at protesters hurling stones and petrol bombs at them. The running clashes started during a midday march and continued through the afternoon. At least 10 people were detained.
A gathering was to be held Thursday night at the spot where Grigoropoulos died.
The policeman, Epaminondas Korkoneas, said he had not aimed for the teen, but that he was killed by a ricochet.
The death of Alexandros Grigoropoulos sparked mass riots in the immediate aftermath in 2008.
The riots lasted for weeks, with cars torched, windows smashed, and shops looted. The policeman was convicted of murder and sentenced to life in prison.
Police deployed more than 2,000 officers in central Athens. His appeals trial is ongoing. A second policeman present at the shooting was sentenced to 10 years, but was granted a conditional release several years ago.
Riot police stand guard as protesters march during an anniversary rally marking the 2008 police shooting of 15-year-old student Alexandros Grigoropoulos, in Thessaloniki, Greece, December 6, 2018.