US police say President Barack Obama's Westside campaign office was vandalized on Thursday night . Police said someone shot BB gun pellets and threw an object into the office located at 6700 block of South Centinela Avenue in Los Angeles. The incident happened just four days before Obama's scheduled visit to the city on Monday. No staffers were in the office at the time of the shooting, the police said. According to authorities, an investigation involving several law enforcement agencies has been initiated.