Seems to me if they wanted to make a profound statement they would have planted the bombs under the grandstands rather than on the street...where the dignitaries and VIPS sat.
However I tend to think if this is terrorism...possible they hired some of our kids to try to pull this off....they do recruit for such a thing...and kids don't think much about what they're doing...they act and run!
If they don't get pressure from the little people, they can't, and if the dignitaries get killed, that doesn't pull the same kind of press as grandmas and kids.
The aspect which makes it "terror" is that it could happen to anyone, anywhere, not just an 'official', otherwise, the ordinary folks have little to worry about except steering clear of pols looking for a photo op.
That just doesn't result in the same political effect, because the next law to come down the pike stripping the masses of their rights (while protecting the elite) won't be greeted as favorably by the people as a law the frightened populace clamors for.