More than a dozen Los Angeles gangs are targeting some of the city's wealthiest residents in a new and aggressive manner, sending out crews in multiple cars to find, follow and rob people driving high-end vehicles or wearing expensive jewelry, according to police. In many cases, they're making off with designer handbags, diamond-studded watches and other items worth tens of thousands of dollars — if not more — and then peddling them to black-market buyers who are willing to turn a blind eye to the underlying violence, police said. In some cases, suspects have been arrested but then released from...