New tactics are emerging in protests over the shooting of a teenager in Greece.In what students say is organised action, a group of about 100 young people surrounded the office of the Mayor of Athens. Elsewhere, demonstrators gathered outside the main prison in the capital and a college building. Clashes broke out in both locations. And, as the country counts the cost of the worst riots in decades, there have been fresh reports of shops being vandalised. Athens woke up to a tense calm, with efforts to clean up what is feared could be up to a billion euros of damage. The conservative government appears to have weathered the storm so far, including yesterday’s general strike at its policies. But, as Prime Minister Costas Karamanlis pledged to safeguard people from violence and help damaged businesses, analysts said his administration’s already low popularity ratings had sunk further. The two policemen charged over the fatal shooting will be held in prison pending their trial. There has been anger that the officer accused of murder did not express remorse to investigators on Wednesday. He says he fired warning shots in self-defence which ricocheted to kill the 15-year-old youth.