NY Times 
April 26, 2013
Nine months before the Boston Marathon bombing, a U.S. counterterrorism task force received a warning that a suspected militant had returned from a lengthy trip to Russia, U.S. officials said.
The warning was delivered to a single U.S. Customs and Border Protection official assigned to Boston’s Joint Terrorism Task Force, a cell of specialists from federal and local law enforcement agencies. The task force was part of a network of multi-agency organizations set up across the country after the Sept. 11, 2001, attacks to make sure that clues and tips were shared.
But officials said there is no indication that the unidentified customs officer provided the information to any other members of the task force, including FBI agents who had previously interviewed the militant.
The man whose return from Russia went largely unnoticed was one of the two brothers who would later be accused of carrying out the April 15 bombing that killed three people and injured more than 250 others near the finish line of the Boston Marathon.