Narco tunnels are hard to detect, extremely lucrative, and cartels have become adept at constructing them — all of which means that tunnel task forces on both sides of the border won't have a shortage of work anytime soon.
A US Homeland Security Investigations (HSI) Special Response Team agent looking into tunnel exit point during an investigation of a cross-border tunnel linking Calexico, California, and Mexicali, Mexico, in Calexico, California, March 23, 2016.