<p>For years, U.S. officials along the southwestern border have done a peculiar dance with local ranchers and other residents who, without the government's help, have captured thousands of illegal immigrants from Mexico.</p>
<p>Publicly, authorities have discouraged citizen patrol groups, which civil rights advocates and Mexican officials have accused of being abusive "vigilantes." But in an approach that the critics say encourages vigilantism, U.S. agents routinely accept immigrants caught by such patrols, and return the immigrants to Mexico.</p>