BOSTON — A man in Orlando, Fla., who was being interviewed early Wednesday morning by law enforcement officers about his ties to the deceased Boston Marathon bombing suspect was fatally shot after he tried to attack the officers with a knife, according to a federal law enforcement official. The officers — who included an F.B.I. agent from the Boston field office and two Massachusetts state troopers — were questioning the man, Ibragim Todashev, about whether he had played a role in a triple murder on Sept. 11, 2011, in Waltham, Mass., which had been one of the biggest mysteries in...