When he was caught selling crack in San Francisco's Tenderloin in April, the Honduran immigrant who called himself Javier Martinez first told police he was 18. Then he said he was 16. Because he insisted he was underage, police were duty-bound to take him to Juvenile Hall, where he would be shielded from deportation under the city's long-standing policy of not reporting juvenile offenders to federal immigration authorities. He was soon put up in a $7,000-a-month group home in Southern California at city taxpayer expense. In short order, he became one of the eight offenders who walked away from unlocked...