Lots of folks could be behind it—A List:
1. Black Radicals like Black Panthers?
2. North Koreans—It was Kim’s Birthday.
3. Radical 99 % people striking the rich white folks.
4. People hitting back for Drone attacks.
5. Red Chinese to distract us?
6. Iranians who do not like our stand on their Nukes.
7. Radical Jews who want to embarrass Obama.
8. IRA Irish Radicals who want to get someone
9. Mafia who wanted a “Cut of the Marathon money”.
10. You name it....
You forgot some more that the gov’t should add: Evangelicals, Catholics, Mormons, Hasidic Jews, Amish, Memmonites, - well, you get the point!
The truth is probably closer to this. Some immigrant or domestic student was hired to plant the bombs which were provided to him. He she or it is probably dead already. And the truth is whatever the government says it is.