The latest leak is that they were pressure cooker IEDs. http://hosted.ap.org/dynamic/stories/U/US_BOSTON_MARATHON_EXPLOSIVES?SITE=AP&SECTION=HOME&TEMPLATE=DEFAULT&CTIME=2013-04-16-12-13-07 I did some research and found this article/blog discussing this IED training in Afghanistan and Pakistan. http://nfttu.blogspot.com/2006/03/pressure-cooker-bombs.html