PHOTOS: Explosions Rock Boston Marathon

(Boston, MA)  --  Investigators reportedly believe a pressure cooker may have been used in one of the bombs that detonated at the Boston Marathon yesterday.  CBS News cites a source as saying one of the explosive devices appears to have been placed in a pressure cooker that was then put into a bag or backpack. 

Using the cookware may have increased the pressure of the blast before it ripped into the crowd watching the marathon.  Doctors are seeing shrapnel and nails in the bodies of the victims.