Interview with runners at the Boston Marathon who saw a bomb squad drill taking place at the event. This is a classic signal of false flag terrorism. That is how it went down at the London subway bombing - bomb squad drill was occurring at the same time. That is how it happened on 911 - FEMA was put in place around the WTC the day before 911. These "drills" are actually used to facilitate the op by having personnel in place to ensure that local policing does not interfere with the operation, and that then there are trained forensics people immediately on hand to mind whatever inconvenient evidence might be laying around in the aftermath.
I am not saying this is incontrovertible evidence of a larger conspiracy, but it is a classic signal. It is why a real investigation and journalistic inquiry is called for.