This is a slab of hard land where four states meet on an international border, far from the centers of official power: Arizona and New Mexico to the north, Sonora and Chihuahua to the south. Little more than a thousand people live here, scattered in the valley towns of Rodeo and Portal and in the mountains. Many of the ranching families have roots going back a century, and they've been joined by new arrivals seeking sanctuary from a cluttered, noisy world. Retirees and birdwatchers live in desert homes hardly visible through the mesquite and cacti. Backpackers traverse the slopes of 9,000-foot high "Sky Island" peaks in the Coronado National Forest, and tourists gape at twisted rock formations in Chiricahua National Monument.

During the Clinton administration, the U.S. sealed off the border to the west, at San Diego, with a high steel wall running some 65 miles inland from the ocean. To the east, the Border Patrol in El Paso established a blockade, Operation Hold the Line, with one agent every quarter mile. Both strategies worked: Illegal immigrant traffic and drug smuggling were funneled between the fortifications. Suddenly, Arizona's 330 miles of border became the favorite route.

Today, thousands of people cross illegally every month through Arizona, either adding to the estimated 400,000 illegal immigrants living in the state or just passing through. Border fences have been erected in Arizona's border towns, while the Border Patrol has focused on the most established illegal routes that bypass fences. But that merely pushes the illegal traffic to more isolated spots, including the mountain ranges around this valley. The local stretch of Mexican border is merely a double rail of welded steel running across the landscape, seated in X-shaped crossbeams sunk into the ground -- no obstacle to foot traffic.

"People thought these mountains would stop the burreros," says Luis Mendoza, a former U.S. Forest Service firefighter, pointing toward the Chiricahuas' sweeping slopes where the drug mules (burreros) scramble through. "Hell, no, it don't stop them. It stops the Border Patrol, though. I seen these guys smoke the Border Patrol when they're being chased." Two years ago, someone broke into Mendoza's house in the valley, stealing food and two prized guns, a .22 and a Colt 1911 from the First World War; the burglar was never caught. Seeing similarities with the Apache wars of the late 1800s, Mendoza says, "They couldn't catch Geronimo in these hills. ... These burreros are walking in the dark; they don't even need the moon."

"Most people that come through here come through these mountains -- volcanic rock the whole way," says Kim Perry, pointing toward the Peloncillos. The volcanic rock formations, along with sand and gravel spilling from the mountains' flanks, are not only hard to cross, they also make it difficult to track people's footprints. Perry's lived here alone for 25 years and says she's figured out how to deal with the growing numbers of illegal immigrants and drug smugglers that use these ranges.

"I have a .38 that I carry on me," she says. And in her house: "A .223, two twelve-gauge shotguns, a four-ten, a .22, two baseball bats and two dogs." The harsh afternoon wind blows her graying blonde hair. "And then I have a cowpusher on the front of my truck to push anybody out of the way. Yeah, I'm prepared." She's decided to take no chances if a stranger approaches her home. "I had a whole bunch of friends that were peace-lovers. They would let the people come in and get water and food and whatever they needed and it became a pathway. So the first time someone came up on my property, they got shot at and I screamed out obscenities like a crazy person and since then, I've only had two or three come back."

Her neighbor, Bonnie Catanzaro, lives a quarter mile away, her house seemingly lost in the wide plain of creosote and mesquite thicket. The elderly widow's home has been broken into twice over the past few years. The first time, someone wrapped a rock in a sweatshirt and smashed out a plate-glass window. The second time, a burglar ate two burritos out of her fridge, put the dishes in the sink, sat on the couch and ate candy, then walked away with various items, including a hand-held video game. After that, the elderly woman installed a thick-gauged wire fence eight feet high, embedded in stone around her front yard. She keeps two enormous guard dogs that might be able to take down a coyote. Or a man. A .357 pistol stays within easy reach.

"I refuse to be caught in my own home," Catanzaro says.

Down the road, near Portal, two men from Chihuahua broke into the home of an elderly couple last January. According to sheriff's reports, the couple was cooking dinner when the two walked in armed with a machete. They demanded money and car keys. Then they duct-taped the 75-year old man and his 74-year-old wife to a chair, took the car and left.

In effect, nonviolent illegal immigrants are being lumped in with troublemakers. Retired Arizona Superior Court Judge Richard Winkler keeps a cattle ranch east of Rodeo, an hour's drive from the border. He has strong opinions about the illegal traffic. "Used to be, you could trust them," he says. "Last few years, it's a little different." He recalls a night two years ago: He was sound asleep in bed. Someone stirred outside, then the front door shuddered and fell open. He ran out the side door, jumped in his car and drove off to call police. A work cabin he keeps up in the Chiricahuas has been broken into so many times that he doesn't bother locking the doors anymore.

"I used to lock people up for this!" he says. "They're just shitheads. Where is the government?"

After Krentz's murder, the Homeland Security Department added 100 Border Patrol agents, extra helicopters and an unmanned aerial vehicle to its forces in the San Bernardino Valley. But those reinforcements are still spread thinly on the land.

The chaos includes bureaucratic and technological glitches. The Border Patrol is organized into sectors, with agents based in numerous stations within each sector, like city cops working in precincts. The border here is supposed to be patrolled by agents from the Lordsburg, N.M., station (part of the El Paso sector) and the Willcox and Douglas, Ariz., stations (the Tucson sector). The Lordsburg station is the farthest away (75 miles) but its agents are the primary responders here. And though the Border Patrol won't admit it, Lordsburg station agents use analog radios, while the Arizona stations use digital. During the initial search for Krentz's killer, agents from the different sectors weren't able to communicate with each other.

The Lordsburg agents have set up a temporary base at the southern end of the valley, a camp comprised of Bedouin-style tents, diesel generators and floodlights. That, along with the reinforcements, has helped some, residents say. "The mix of manpower, physical barriers, air support and technology is the right formula," Sheriff Dever insists. "There simply is not enough of it and some changes in strategy could lead to better use of those systems. Where the enforcement effort comes up woefully short is at the prosecution end." Often, people from the other side of the border who are arrested here are just returned to the other side.

Rumors fly around the ambush of Krentz. Some locals think the killing was the result of a personal conflict, not a random encounter. The day before the shooting, for instance, Krentz's brother called in a dope load to the Border Patrol. Agents seized 290 pounds of pot and eight illegal immigrants. That leads some to believe that Krentz was killed in revenge.

Krentz didn't seem to be the kind to make enemies. He'd mind his own business but he wouldn't back down, says Louis Pope, Krentz's brother-in-law. Sitting in the shadows of a mesquite, the tall, rangy rancher picks at the planks of an old table and slams a hard hand down to make his points. "Rob was a humanitarian," he says. He recalls two instances when the man helped Americans stranded in the mountains. "One time these two men came up to his house, needing an alternator for their truck. Rob gives them the keys to a truck and tells them to drive to Douglas and pick one up!" He pounds a fist on the table. "And then, he installs it for them! Yes, he did!"

Another time, Krentz saw two women walking with some kids; he gave them a ride to town and wouldn't take a dime. He also helped illegal immigrants in his own way: He kept water spigots readily available for those who needed a drink as they passed through. It was better than having his water lines slashed by those who were desperate, and he didn't fancy the idea of anyone dying of thirst. Pope recalls, "He'd say, ‘They're walking past my home to go work in yours.' "

Michel Marizco is an organized crime reporter working along the U.S.-Mexico border. He runs a Web site, borderreporter.com, and lives in Tucson, Arizona.