From Wall Street Journal and this Fox article http://www.foxnews.com/us/2013/08/06/lawyers-said-boston-marathon-bombing-suspects-had-befriended-anti-us-conspiracy/
The bombers befriended a guy that had a head injury and then started acting crazy, believing in anti-US conspiracy groups, like an "Alabama-based publication that uses a Confederate flag on its website and a weekly publication that the Southern Poverty Law Center calls anti-Semitic." Some of his publications were found at the Boston Bombers apartment.
Great! Linkage between crazy Muslims and crazy white supremist groups!
Or, people that believe in anti US conspiracies are like this guy that had brain damage and acted child like.