Hollywood Boulevard is the West Coast equivalent of Times Square, an urban reclamation project that transformed a strip once notorious for crime, drug-dealing and prostitution into a tourist destination, a thriving night life district and the home of movie premieres and the Academy Awards. But over the past month, two high-profile crimes — a fatal stabbing of a tourist by a homeless person and a robbery spree by a gang that bounded past people gawking at the Walk of Fame — have threatened this carefully cultivated and civically critical reinvention, worrying community leaders and presenting an early challenge to this...