Acting on tips, Mexican authorities found the entrance of a 2,400-foot tunnel running from a small warehouse near Tijuana airport to a large warehouse in Otay Mesa, San Diego, and agents entered the passage on Wednesday 25 January 2006.[1][2] US agents had hunted the tunnel for over a year with classified military detection equipment without finding it.[1]

The tunnel ran nearly half a mile through sandstone and compacted sand, fitted with lighting, ventilation and groundwater drainage, with chest-high water at its deepest point more than nine stories down.[1] Investigators called it the longest cross-border tunnel in US history and the work of a well-funded smuggling group.[1] The head of the San Diego DEA office named the Arellano-Felix Tijuana cartel as the usual suspects.[1]

Two tons seized, no arrests

Mexican agents seized two tons of marijuana on the Mexican side while their US counterparts found 200 pounds at the Otay Mesa end.[1][2] Neither side reported any arrests.[1] Agents said their work was just beginning, poring over the site for fingerprints, DNA, phones and computers to link the builders and operators.[1] Activity at the 48,222-square-foot Otay Mesa warehouse had stopped abruptly the previous October after busy months of trucks moving through its twelve docks.[1]