An Immigrant Underground

Recently discarded blankets, jackets and clothing line a 3-ft-high drain culvert. Illegal immigrants and drug smugglers crawl through and exit to a street above.  (Don Bartletti / LAT)

Inside the sector command center, Border Patrol agent Abelardo Vasquez radios line officers of a suspicious person. TV monitors display infrared images from video cameras mounted on poles along the borderline.  (Don Bartletti / LAT)

Border Patrol agent Jim Amstedz inspects a drain tube for migrants. Discarded jackets are evidence that a group climbed into the tube and out onto the street above. The cavernous drain tunnel leads to Mexico.  (Don Bartletti / LAT)

Searching for smugglers a mile inside a drainage tunnel, Border Patrol agent Jim Amstedz yanks open a steel gate that defines the U.S./Mex. border. Scott Connors (left) and Scott Wencel hold weapons at the ready.  (Don Bartletti / LAT)

Remote television cameras mounted on a pole helps U.S. Border Patrol authorities keep an eye on the U.S./Mexico borderline in Nogales. Images from dozens of the remotely moveable and zoomable cameras along this border are monitored in sector headquarters several miles away.  (Don Bartletti / LAT)

Border Patrol agents Scott Wencel (left) and Jim Amstedz look for breaks in the Grand Avenue drainage grate. Mexican smugglers often puncture it to pass people and drugs into the U.S.  (Don Bartletti / LAT)

Just inside the U.S. side of the borderline, Senior Border Patrol agent Pat Cory welds a storm drain grate. Smugglers regularly cut the grate to funnel drugs and people inside. They crawl as far as a mile and exit manhole covers throughout the border business park.  (Don Bartletti / LAT)

About a mile north of the borderline, Border Patrol special operations supervisor Matilde Torres exits a drainage tunnel known to be used by smugglers to sneak people and drugs into the U.S.  (Don Bartletti / LAT)

About a mile north of the borderline, Border Patrol special operations supervisor Matilde Torres inspects a drainage tunnel often used by smugglers to sneak into the U.S. Agent Joe Perez peers through an open manhole where migrants exit to the street of the industrial park.  (Don Bartletti / LAT)