In the wee hours on April 25, a Predator B drone crashed into the desert floor near Tucson, Arizona, temporarily grounding one of the most expensive high-tech programs yet deployed in a burgeoning “virtual wall” that’s taking shape on the U.S.-Mexico border. Since its launch in September 2005, the unmanned aerial vehicle, or UAV, had helped the U.S. Border Patrol capture 1,700 illegal immigrants attempting a crossing in the area, according to the agency, which is eager to replace the $14 million aircraft. Full Story