There is a new theory, (emphasis on theory) that the bomb on the bus went off prematurely (or the terrorist was late) and that is why the 4th bomb did not hit a subway car. This makes sense in many ways, unfortunately. But terrorists do have to travel to their destinations, making it easier to spot them.

Sir Ian Blair, the Metropolitan Police commissioner, said there was no evidence that the carnage was the work of suicide bombers, although it is thought that a terrorist could have been among 13 people killed when a device, possibly intended for the Underground, exploded on a bus in Tavistock Square.

Two of the devices, at Liverpool Street and Edgware Road, are thought to have been left close to the double doors of the carriages and they could have been operated with a timer or remotely. While suicide bombings were not being ruled out, police were working on the theory that a terrorist cell of at least four people planted the bombs.

At least now they tipped their hand to some degree, and possibly there is more evidence on the body of the late terrorist (pun intended).