A 13-year-old boy has been charged with murder over the fatal stabbing of a 36-year-old man in Mount Druitt, in Sydney's western suburbs, on Friday evening. A 16-year-old was also charged as an accessory after the fact, and both were refused bail; police say at least two others allegedly involved are still being sought. Police said the man, who was on his way home from work, was attacked after a second group took offence at his friendly encounter with a group of young people, and a senior officer called the killing "absolutely senseless".