A forensic expert uses a camera as shoppers pass behind a police barrier at the scene of a murder on Oxford Street in London December 27, 2011. An 18-year-old was stabbed to death in front of horrified shoppers on Monday during a fight between two groups of youths on London's Oxford Street, one of Europe's busiest retail districts which was packed with thousands of bargain hunters. REUTERS/Finbarr O'Reilly (BRITAIN - Tags: CRIME LAW SOCIETY)