Investigators now believe a massive blast at a Tennessee military explosives facility killed 16 people, officials said on Saturday.Officials had previously said 18 people were unaccounted for in Friday's explosion, but two people whose vehicles and personal items were found at the scene were not actually there when the blast erupted, Humphreys County Sheriff Chris Davis said at a press conference.The explosion, which was felt for miles, leveled a building at the 1,300-acre (5-square-km)