I'm waiting on more information before I start the wailing and gnashing of teeth. Something a bit weird about this one. If it was one of the organised terror groups they would have claimed responsibility by now. All we know right now is that it was a suicidal nutter with a homemade device. They haven't released his name, background or religious inclination yet.
The obvious terrorist suspects often take a while to claim responsibility, but we should not ignore the likely inspiration for this atrocity, to do so is just burying our heads in the sand.