Assistant Commissioner John Yates had been under pressure for his ties with the News of the World, the now-defunct tabloid at the center of the scandal. His move follows the decision by Scotland Yard chief Paul Stephenson to step down over criticism of the links between senior police officials and Rupert Murdoch's media empire.Following the resignation of his boss, Scotland Yard chief Paul Stephenson, a second senior British police officer quit Monday amid the phone-hacking scandal that has reached into the highest levels of public life in Britain.