'Although no group has claimed responsibility for Monday's deadly bomb blasts at the Boston Marathon, a leading al-Qaeda ideologue last year recommended that jihadists in America include sporting events in their list of prospective terror targets.
Writing in the online magazine of Al-Qaeda in the Arabian Peninsula (AQAP),Inspire, the terrorist known as Abu Musab al-Suri listed what he called "the most important enemy targets."
"This is done by targeting human crowds in order to inflict maximum human losses," he wrote. "This is very easy since there are numerous such targets such as crowded sports arenas, annual social events, large international exhibitions, crowded market-places, skyscrapers, crowded buildings ... etc." '
More here http://www.familysecuritymatters.org/publications/detail/al-qaeda-propagandist-called-for-attacks-on-sports-events-boston-terror