The heist cut through hushed corridors with a speed and ease that humiliated a nation. Authorities are now racing against their own clock. In the space of just seven minutes in the casual daylight of Sunday morning, four suspects stole nine pieces of France’s crown jewels from the Louvre. They robbed not just the most visited museum in the world, but also the French people themselves, the government said Monday. Officials are now scrambling to reassure the public about security at key cultural sites — and find the jewels stolen from the museum before they can be broken up and melted down...