British actress Gemma Chan has told a court of the terrifying moment she saw a killer stab a homeless man at a London tube station. The Sherlock star told the Old Bailey she locked eyes with murder suspect Frederic Russell outside Putney Bridge station after he allegedly knifed Colin Hammond last October (12). Explaining how she was tending to the victim when his attacker returned, Chan said, "I got about six feet from him and he was groaning and holding his left side of his neck. I asked if he was all right. "At this point the man reappeared on the corner. He at first peered around the corner looking at the older male on the ground. We stared at each other for about three seconds and then the road started to fill with people as a train had arrived at the tube station." French national Russell, 28, was charged with murder, but officials found him unfit to appear in court. A jury will now determine whether he killed the 65 year old. The trial continues.