Of course.
Boston is well known for its extreme right wing groups - being bright red on the voting map and all.
They could round up all of the extreme right wingers in Mass in a Smart Car.
Well, obviously the bomber has to be an evil rightwing racist sexist fascist bigot homophobe since Boston is a liberal city and the Boston Marathon is a liberal event and typically marathoners are either skinny liberal men or nonmenstruating feminists or liberal gay activists and who all shop at Whole Foods afterward while cheering the death of Margaret Thatcher.
Too easy.
;^)