An anti-war march against the U.S. policy on Iraq by about 500 Canoga Park High School students turned ugly Wednesday when some in the crowd started looting a gas station convenience store and disrupting traffic. A group of students who skipped class to participate in the lunchtime protests stole candy bars and knocked over displays at the Mobil gas station at the corner of Topanga Canyon and Victory boulevards, officials said. Five of them were detained on suspicion of vandalism and theft, said Officer Jason Lee, a police spokesman.