Boston Marathon bombs seem to follow widely available recipe , experts say . Score: 6 Al Qaeda , U.S. right-wing extremists use hard-to-trace bombs , experts say .
Boston Marathon bombs seem to follow widely available recipe , experts say . `` Lone wolf '' devices worry the intelligence community because there 's `` no trail , no intelligence '' Al Qaeda , U.S. right-wing extremists use hard-to-trace bombs , experts say .