This post was made by fatboy on airgunshack but it hought it was appropiate and gives us alls omething to think about:
It is a very sad day indeed. We actually got off very lightly in terms of casualties, it could have been alot worse. Fortunately, the stations they attacked were very close to major hospitals.
It is still unclear if they were suicide bombers or just bombs planted on the trains, however most trains exploded after entering the tunnel for 100 yards. I suspect that the explosive they used was "home made" and not military c4,c3, semtex. looking at bbc photo's( especially