Despite the extensive effort that goes into constructing narco tunnels, and the huge loads that travel through them, they are often hard to detect. "US-Mexico border is literally riddled with tunnels, and the big problem is that there's no technology that can detect those tunnels," Vigil told Business Insider. For every tunnel found, about 10 go undetected, he said.
The entrance of a tunnel connected to the Altiplano Federal Penitentiary and used by drug lord Joaquin 'El Chapo' Guzman to escape, is seen in Almoloya de Juarez, on the outskirts of Mexico City, July 12, 2015.