Experts who examined a cache of long-lost photos from the 1930s Spanish Civil War say it yielded a lot of new information, but failed to solve the biggest mystery whether legendary photojournalist Robert Capa took the famous picture of a man at the instant he was killed by a bullet. Answering that question was a principal goal of curators at the New York-based International Center of Photography when they first delved into the so-called Mexican Suitcase, a collection of 4,300 frames shot by Capa, his companion Gerda Taro and close friend David "Chim" Seymour. The negatives, long believed to have...