NBC banner: More than 100 being treated after Boston Marathon explosions.
I am not sure, but if I look at the photo’s I see a lot of people with injured legs. I suspect the bomb was a copy of the IRA nailbombs:
http://www.lexpev.nl/grenades/europe/unitedkingdom/iranailbomb.html
If it was in a bag on the sidewalk with the bomb in it and standing upwards it would create this kind of injuries by the fragments of nails that fly sideways, in this case at street level.