US officials knew about the potential danger of Boston Marathon bomber Tamerlan Tsarnaev, according to a soon-to-be-released Congressional report—but a spelling error led them to miss his frequent flights out to Dagestan for terror training. […] In March 2011, Russian intelligence agency FSB notified the FBI with concerns about Tamerlan Tsarnaev and the Tsarnaev family, which had emigrated to Massachusetts nearly ten years earlier. In the letter, FSB included contact information, with addresses and phone numbers, for many of the members of the Tsarnaev family, including Tamerlan and his mother, and warned that Tamerlan was gaining a reputation for associating...