ATHENS, Dec. 21 (Xinhua) -- An anti-racism rally in central Athens's Syntagma Square on Sunday led to a violent confrontation between the protesters and riot police, the latest of a series of clashes triggered by the death of 15-year-old boy Alexis Grigoropoulos, who was killed by police on Dec. 6.

    A group of people tried to deposit bags of rubbish at the foot of a new Christmas Tree, erected in the square by the Athens municipality to replace an old tree which was torched during the riots following the boy's death. Police used tear gas to disperse the protesters.

Riot police clash with demonstrators during riots outside the Athens Polytechnic Dec. 20, 2008. (Xinhua/Reuters Photo) Photo Gallery>>>

    According to Athens News Agency, six police vehicles were torched by unidentified hood-wearing assailants wielding petrol bombs in the west Athens district of Nea Philadelphia early Sunday morning. The vehicles were parked outside the building of the police accounting department, which also suffered damage in the attack.

    On Sunday rioting and violent clashes continued in the area around the Athens Polytechnic, National Technical University of Athens, with protesters again lobbing petrol bombs at police.

    Greek police experts on Sunday carried out an on-site forensic investigation at the spot where Alexis Grigoropoulos was shot dead, trying to gather more evidence related to the case.

    The investigation lasted about two to three hours and was conducted in the presence of the 9th examining magistrate who is in charge of the case.

    Athens News Agency said that the additional specialized investigation, which seeks to find evidence to complement the findings of the ballistic report in light of eyewitness accounts claiming that the officer was aiming directly at the group of youths, was requested by lawyers representing the family.