I cant see who hopes to benefit from this type of terrorism, after all "they" have tried before and not got anywhere.
Thankfully, the loss of life,whilst unacceptable, was not as bad as it could have been.
I applaud those who helped the injured from all walks of life, particularly as another bomb was detonated only a few seconds later. If the "terrorist" had set the second bomb in the same place, it would have killed/injured them too. Apparently this is a terrorist trait - explode one bomb shortly after the first to kill as many helpers - be they police,medically trained,civilians,military etc.
Lets hope forensics turn something up.