Not every illegal immigrant in the United States snuck across the border. A very large number, perhaps as many as 5.5 million, entered legally with visas and then never left.
But unlike the hundreds of thousands of illegal immigrants apprehended at the border every year, very few visa violators are ever caught.
The Border Patrol's Tucson sector, the busiest in the nation, logged 112,488 apprehensions last fiscal year. In comparison, federal agents in Arizona tracked down and arrested 27 people who had overstayed their visas.
Visa violators represent nearly half of the 11 million illegal immigrants in the country. But they have been largely ignored amid a national clamor to secure the border, fueled in part by Arizona's tough new immigration law, the killing of a southern Arizona rancher and worries that cartel violence in Mexico could spill into this country, analysts and experts say.