You've got people on the right saying it's likely an Islamist terrorist.  You've got ultra-libertarians like Alex Jones saying it's a false flag attack by the government.  And you've got left wingers saying it's probably an ex-military milita person or a Tea Partier (citing that today is Tax Day).  Everyone has their theories, but expressing these theories only cause more anger and pain.  Why not focus on promoting ways to help the victims (give blood, etc.) instead of speculating.  That's the job of the police and FBI.