The murder:
The police says that a police car at Exarchia was attacked by anarchists with rocks and bats and one of the cops shoot in the air (or ground) to scare them off and the bullet hit somewhere, changed course and hit the boy on the chest. However there are eye witnesses that state that there was no attack, only shouts against the cops and that the cop took a straight shot on the boy. The media also mentioned that there are leaks from inside the police verifying the eye witnesses but the official police statement denies that.

The aftermath:
After the murder of the 16 year old boy thousands of people filled with rage gathered and demonstrated in various places in Athens and other greek cities and started rioting and clashing with the police. There are reports about thousands anarchists, leftists and others that took the streets, also about tens of police departments attacked and hundreds of banks, cars, governmental buildings and shops smashed and set on fire. The clashes kept on until the early hours of Sunday morning.
Tomorrow, Sunday, demonstrations are taking place in tenths of greek cities and in some other European cities.

The history:
In 1985 also at Exarchia in central Athens, a 15 year old boy, Michalis Kaltezas, was shot dead by a cop, this time with a bullet in the back of his head. Again back then the reaction was very strong by the anarchists, the leftists and plain people disgusted but the police brutality. The classes with the police lasted for days.

The first pictures: http://athens.indymedia.org/front.php3?lang=el&article_id=933717
some articles (in english): http://en.wikinews.org/wiki/Killing_of_a_15_year_old_student_in_Greece
http://www.indymedia.org.uk/en/2008/12/414458.html
http://www.indymedia.org.uk/en/2008/12/414470.html?c=on#comments
http://athens.indymedia.org/front.php3?lang=en&article_id=933218
and it also in all the major corporate news sites.