WASHINGTON – U.S. military investigators found no conclusive evidence that an Afghan officer who killed eight U.S. airmen and one U.S. civilian during a meeting in Kabul in April had ties to the Taliban, according to a report released Tuesday. But the gunman, who shot each of the Americans multiple times after arriving for a routine meeting at an Afghan air force headquarters compound, previously had vowed to "kill Americans," the report said. The incident — among the deadliest of its kind during the 10-year-old war — showed the dangers faced not only by U.S. troops on Afghan battlefields but...