Doug asked, what is to be Done?
1) The US government can't prosecute the guilty because they are dead. The government can go after the secondary conspiracy and support groups, if the security apparatus can identify them, and then attempt to prosecute them. This will probably happen at some point, but this option seems to offer little public satisfaction, let alone anything so lofty as justice.
2) The US govt can't present a case against foreign individuals, political groups or foreign states who may have helped plan and pay for the terrorist attacks before the International Court at the Hague, because the US has not ratified the UN protocols and resolutions required to become a member of the court. Only members can prosecute cases before the court.
3) The US govt can't enlist powerful allies in the Islamic world to identify, apprehend, and assist in developing a case against possible suspect individuals and groups involved in the attacks, for the simple reason the US has no allies in the Islamic world.
4) There are no means that are either legal or legitimately recognized by the international community of nations to respond to these attacks.
5) Assuming that a response is necessary, then by default, the US government has to engage in the random slaughter and destruction of war in the hope that local officials will turn over the suspects when those quasi-official groups determine they can no longer endure the de-stabilizing effects of the killing and destruction.
But these are issues and difficulties for the Empire to consider. I have no reason to assume or serve the needs and interests of the US government and its Empire, since the government has shown absolutely no interest in serving my needs as a citizen.
Under the Social Contract theory of governance, the primary obligation of government is to provide for the security and protection of its people. Thus, the US government has abrogated its social contract twice in less than a year: first by disenfranchising a majority of its voters, and second by failing to protect and secure people under its governance from massive and grievous harm. Soon, if the government can manage it, it will add to this list by denying people under its protection some measure of their civil rights, due process, and habeas corpus in the name of protection which it has shown itself to be incapable of providing.
For those people who feel some obligation to support the destruction and slaughter in Afghanistan in the name of justice, consider that the US government is not engaging in war in order to protect your needs or interests, but it own interests and power. Consider that your basic need for security, your civil rights, as well as your vote have been dismissed out of hand.
We have all been called upon to support the government in its actions, and we have been lectured by our political leaders on our moral duty to do so despite their absolute and demonstrable contempt for our interests, security, rights, and votes.
In my view one contemptible turn deserves another.