US Customs and Border Protection Process

OTAY MESA, CA - MARCH 6: Mexican nationals apprehended while crossing the U.S-Mexican border illegally wait in a holding area at the Brownfield Customs and Border Patrol (CBP) processing center on March 6, 2006 in Otay Mesa, California. Mexican nationals caught illegally crossing the border are sent back and classified as "voluntarily returned" without any charges if there is no outstanding criminal case on record. The Otay Mesa border area comes under the jurisdiction of San Diego and comprises 66 miles of land border with Mexico. This is a popular crossing area for the Mexican mafia controlling human smuggling. It is estimated that some 6.3 million illegal Mexican immigrants live in the US and some 485,000 undocumented Mexican immigrants enter the US annually. The US government estimates 11 million illegal immigrants reside in the US (Photo by Robert Nickelsberg/Getty Images)