Is there any doubt at all?
I mean, all the signs point to it being al Qaeda.
1) Suicide attacks. (Although this hasn't been demonstrated yet, the fact that at least one of the tube bombings was done when 2 trains were together in a station points to it having a human trigger.)
2) No warning.
3) Coordinated, nearly simultaneous bombings.
4) Civilian victims.
5) Highly visible.
6) Timed to cause maximum economic damage and confusion (morning rush-hour).
Etc.
It may be a new cell, but it has all the markings of an al Qaeda group, IMO.
Cheers,
Scott.
