Tools are seen in a tunnel under the U.S. Mexico border which starts in Tecate and runs into southern California, December 4, 2007, after it was discovered on Monday by law enforcement agencies. Gunmen killed the police chief of Tecate, a Mexican city bordering California, on Tuesday by shooting him some 50 times in an apparent revenge attack after police found the drug-smuggling tunnel under the border. REUTERS/Jorge Duenes (MEXICO)