Patrolling South Texas for Illegal Immigrants

"Our house is like a trap," she says. "They don't know a border patrolman lives there. If they come, they're gonna get caught." Yolanda, whose parents were both born in the American Southwest, says Diaz rarely talks about the stresses or challenges of his work when he's home.

Manuel Sauceda, a Border Patrol intelligence agent and father of two who grew up in Laredo, says he learned to deal with emotionally charged experiences early on. "My supervisor told me to leave it at work—the arrests, the car rollovers, all that," he says. "It's not you putting people in those situations, it's them. They chose. You're here to take care of yourself and your family. Do your job, process it and leave it at work. That's how I've looked at it ever since."

While catching immigrants may at times be hard on the conscience, arresting coyotes and drug smugglers is not.

When Diaz leaves his large office and administrative duties for the field, he spends much of his time driving up and down I-35, eyes peeled for trucks packed with illegal immigrants or drug loads. "You can tell by how heavy the trucks are loaded, by how they bounce on the road," he says, scanning the highway before him while he drives. "The latest trend we're seeing is F450 and F550 Ford trucks. The smugglers want to blend in with the local population, and lots of the ranchers and hunters drive those." The trucks used to drive loads and smuggle immigrants are usually stolen, most often from Houston and Dallas.

The day before, Diaz's agents spotted a Ford truck that looked to be riding low. They followed it and ran the license plate, but before they could pull the truck over the driver accelerated, busted through the barbed-wire fence along the highway and careened into the brush. This is called a bailout, and it happens more often than you might think. Usually the drivers—migrants or drug smugglers or both—rumble through the tangled mesquite and cactus until the vehicle gets stuck and they can drive no farther. Then, they take off on foot. Other times, the driver leaps out of the speeding vehicle without even hitting the brakes, leaving the passengers to jump or else risk remaining in the unmanned car.

"I've seen a lot of fatalities," Diaz says. "They'd jump out and fall under the vehicle. Once, north of Highway 21, some people ran into the brush and others ran across the median. This 17-year-old girl got hit by an 18-wheeler." He shakes his head. "It was bad. The agent that took that one was new—he was pretty traumatized."

The truck Diaz's agents followed off the highway right before my visit didn't get far. The driver abandoned the vehicle and ran, but with help from Border Patrol helicopters, he and his co-pilot were soon spotted and arrested. It turned out six undocumented immigrants had been riding inside, sitting atop bundles of marijuana. The week before, agents in a neighboring county stopped an 18-wheeler loaded down with more than 5,000 pounds of pot. The street value was more than $4 million.

Diaz pulls up alongside an 18-wheeler stopped in the median. It's marked Dollar General. The man behind the wheel tells Diaz they're changing drivers.

"It's hard to tell the good guys from the bad guys," Diaz says as he drives away. "But when they're driving loads, sometimes they get facial twitches, or they hold the steering wheel like this." He grips the wheel hard. "You look at the jugular and it's just pumping."