Responding to reports of a disturbance out by Silver Bell Mine road, officers encountered a grisly scene. Two shot dead in a Dodge pick-up, a woman in the front seat, a man sprawled in the back seat. A while later they found a third body, shot in the head and dragged into the desert.

No one knew who they were.

Investigators quickly learned the truck had been stolen in Phoenix earlier that day. The victims had been smuggling about two dozen "illegals" north at the time of the shootings. It made no sense.

When officers tracked down two of the assailants at a campsite a half-mile south of the shootings, the truth came out. It had been a mistake.

The shooters had been holed up in the desert for days, one of them explained, sent there by a drug cartel to rip-off a shipment from a rival gang. They had just hit the wrong truck.

The Silver Bell killings came in 2007. It was a wake-up call for the Pima County Sheriff's office: Their turf was now the path of least resistance for those trafficking in drugs and people.

Some years earlier, officials had beefed up enforcement along the San Diego border sector. Smugglers changed routes, making Texas their primary trade lane. Then a strong federal, state, and local crackdown made the Houston corridor too hot.

The route shifted again. Today, according to George Heaney, a bureau chief in the Pima County Sheriff's Office, the Tucson Border Sector is the busiest super highway for moving drugs and people north -- and money and guns south.

That new reality is reflected in Heaney's county jail. Three hundred of its 2,000 inmates are in the U.S. illegally. They haven't been picked up for immigration violations, though. They are all charged with serious felony beefs.

Many are foot soldiers in the battle among drug cartels -- a war that has spilled north of border. Most of the violence comes from one group of "bandits" preying on another. They let their competitors do the hard work of humping drugs across the border, then try to rip-off one another's "stash." They favor automatic weapons and high-powered rifles. "Fortunately," one deputy told me, "We haven't seen hand grenades and some of the heavier stuff they use south of the border." Yet.

Though it's mostly bandits shooting up bandits, the Pima County Sheriff's office could not just idly watch a drug war rage. But they didn't have to enter the fray alone, either. To combat the border violence most effectively, the office forged a strong partnership with federal and state authorities.

Heaney says the single most important development in that partnership was beefing-up the Border Patrol in the Tucson Sector -- made possible when President Bush and Congress doubled size of the Border Patrol. But Heaney's department made an important contribution, too. It created a border crime unit.

In part, the border crime unit has been effective because of assistance from the Department of Homeland Security. Thanks to DHS, the unit fields its own mini-air force: a helicopter and two small fixed-wing craft that let the sheriff's take the high-ground to hunt down smugglers. The Border Patrol has assigned two full-time troopers to work with the county unit.

Pima County offers a valuable lesson in how to battle the cartels. Since 9/11, Washington has poured billions into homeland security grants, yet it's not at all clear that this spending spree has done much to improve national preparedness or security.

The grants have become exactly what the 9/11 Commission warned against: "pork-barrel" funding mechanisms. Taxpayers would get far more bang for their Homeland Security bucks if more of the money was channeled where it's really needed -- like cooperative law enforcement initiatives to protect our communities along the southern border.

James Jay Carafano is a senior fellow at The Heritage Foundation and the author of GI Ingenuity: Improvisation, Technology and Winning World War II.