still speculation but:
all underground devices were timed.
not suicide bombers.
the bus detonation was also timed but it was 'in error'.
because of the earlier detonations, and the subsequent closing of
the stations and redirection of bus services, its believed that the
would-be bus-bomber was redirected to take a bus instead of the
underground.
it seems that perhaps they had no control over the timing of the
device and it detonated in a not-well placed position [ie. based on
other 'bus-oriented' detonations, they try to place themselves in
the middle of the bus to achieve maximum carnage].
instead it detonated where they sat, at the back of the bus on the
top.
still, thirteen people lost their lives on that bus, many more
injured, maimed, scared.
but it seems that all detonations were destined for the
underground, left in baggage near doors. the bus detonator was
effectively too late to get on the underground.
they are still removing bodies from the carriage inbetween kings
cross and russell square, where there is some structural damage to
both carriage and tunnel.
most main sections of the underground are very deep, and their
construction period is quite old, and so they did not plan for the
cunduction of communications of mobile phones when constructed,
therefore there are many sections of the underground, nearly all
within the central london area, that have absolutely no
communications possibilities over civilian mobile phone.
the piccadilly line at russell square is around 67ft deep.
therefore detonation of bombs via mobile phone is an impossibility,
unlike the madrid bombings.
