I also highly doubt that a handful of people were planning to shoot up a government building in hopes to start a race war.
To continue - just finished reading a scholary text on 'lone wolf' or leaderless resistance terrorism. In the section on Islamic cells in the west, Al Qaeda manuals recommend using the easy to access American guns laws to arm oneself for such lone wolf actions.
One plan of Al Qaeda is to socially disrupt the USA fabric. Hassan was a prime example. Others have been found the USA.