source told fox news on the condition of anonymity pause they are not authorized to speak on the investigation saying the bombs had line of sight with a speed controller as the trigger. based on an f.b.i. and homeland security intelligence bulletin they relied on remote toy cars. the range of the toy car components in boston is not public, it s typically 250 yards or less. significantly the national security source also confirmed that remote controlled parts are not part of inspire magazine, the al-qaeda web magazine is how to guide to build bombs. working theory that one or both brothers triggered the debt nations, a third party in the crowd has not been ruled out, but there is no evidence a third party at this time. the f.b.i. is reviewing the brothers computers for domestic contacts in the plot making.