A tiny motorcycle bomb did this much damage? Larger than a typical car bomb!
YouTube - Shattered windows, blasted cars as bomb explodes outside court in Greece
It had to be a compact high energy substance, such an explosive as only a government would have access to.
What government would want to destabilize a European government?
The recent fire bombs and protests in Greece seem to be lead by Communists.
I suspect the Mossad.