A new study of images apparently from the Syrian attack last month concludes that the rockets delivering toxic sarin gas to neighborhoods around Damascus held up to 50 times more nerve agent than previously estimated, a conclusion that could solve the mystery of why there were so many more victims than in previous chemical attacks. The study, by leading weapons experts, also strongly suggests that the mass of toxic material could have come only from a large stockpile. American, British and French officials have charged that only the Syrian government and not the rebels was in position to make such...