It’s one of the strongest opioids in circulation, so deadly an amount smaller than a poppy seed can kill a person. Until July, when drug users in the United States started overdosing on carfentanil, the substance was best known for knocking out moose and elephants — or as a chemical weapon. Despite the dangers, Chinese vendors offer to sell carfentanil openly online, for worldwide export, no questions asked, an Associated Press investigation has found. The AP identified 12 Chinese businesses that said they would export carfentanil to the United States, Canada, the United Kingdom, France, Germany, Belgium and Australia for...