Hunting for Barcelona's Notorious Street Thieves; Known as a haven for petty crime, the city is trying to reverse its reputation as a pickpocket's paradise.

It's a balmy Friday afternoon before Valentine's Day in Barcelona, and even in winter, Las Ramblas, the city's tree-lined promenade, is packed with people: teenagers dressed as devils for Carnaval, toddlers riding on their parents' shoulders, vendors flinging annoying LED toys into the sunny sky. February may be a slow season for tourism in Spain, but there are still plenty of sightseers stumbling around, munching on patatas bravas and digging into their fanny packs for cash, sunglasses and wipes...