It is quite interesting that you mention that as I was thinking WHO placed those two other bombs we heard about.
Remember we were told there was a controlled explosion done about an hour later??? Whatever happened to that? WHO put those ones out there...?
We have been told there were two explosions, nothing more, period, two explosions and no more mention of the "controlled" explosions, for some reason that has been shoved under the rug. The other interesting thing is that there's a coach who said that just before the bombs went off there were announcements saying to "stay calm, this is only a drill". Interestingly enough, there have been multiple people (runners, spectators) interviewed and not one of them has mentioned any announcement about a "drill".