Honestly, it would not suprise me if it were a homocide bomber. I just always figured they would hit the US first.
Sky News is reporting that the bus was probably blown up by a homicide bomber, but it has not yet been confirmed by Scotland Yard. They are more interested in trying to trace the particles of the explosives used, as if they were not homicide bombers then they are still at large and that is of major concern. Source: FNC news crawl.