Pedro Guzman has been an American citizen all his life. Yet in 2007, the 31-year-old Los Angeles native — in jail for a misdemeanor, mentally ill and never able to read or write — signed a waiver agreeing to leave the country without a hearing and was deported to Mexico as an illegal immigrant. For almost three months, Guzman slept in the streets, bathed in filthy rivers and ate out of trash cans while his mother scoured the city of Tijuana, its hospitals and morgues, clutching his photo in her hand. He was finally found trying to cross the border...