U.S. Border Patrol agents Christopher Knab, left, and Marlan Holland walk April 5, 2007, near the exit of the Grant Tunnel in downtown Nogales, Ariz. , which connects to drainage systems in Mexico. The tunnel was one of two storm drain tunnels constructed by the Army Corps of Engineers in order to alleviate flooding in the area. The Border Patrol has special tunnel teams that specialize in operating in low-light conditions and close-quarter encounters. AP Photo logo AP Photo 33 months ago

U.S. Border Patrol agents Christopher Knab, left, and Marlan Holland walk April 5, 2007, near the exit of the Grant Tunnel in downtown Nogales, Ariz. , which connects to drainage systems in Mexico. The tunnel was one of two storm drain tunnels constructed by the Army Corps of Engineers in order to alleviate flooding in the area. The Border Patrol has special tunnel teams that specialize in operating in low-light conditions and close-quarter encounters.