Agents Discover Tunnel Below Mexican Prison Mexican investigators have found a 40-yard (meter) tunnel that inmates chiseled underneath a prison in the northern city of Chihuahua in an apparent effort to escape. State prosecutors' spokesman Carlos Gonzalez says the 30-inch (76-centimeter) diameter tunnel was lit and almost finished with just 16 feet (4.8 meters) left before reaching the desert outside. Gonzalez told The Associated Press Friday that up to 250 of the 1,800 inmates housed at the medium-security penitentiary on state charges could have escaped through the underground passageway. He says it took between two and 2 1/2 years to build the underground passage using chisels and a sledgehammer. Agents also found an AK-47 rifle inside the tunnel.