I may well be wrong (about anything and everything) but my first reaction is that it’s an ethical mistake and a foolhardy one too to try the (alleged) Sep 11 terrorists in civil court.
The ethical mistake: Civil courts are appropriate for trying people within your society who have broken a social contract, actual or implied. Violent destroyers of your society from outside your society, justifiable or unjustifiable, have not broken the social contract and don’t belong in civil court. They might belong in a court administered by a real “United” Nations who could be an appropriate distributor of justice for people who have broken the world’s social contract, assuming you could imply that there is one. But that is unlikely to happen.
The foolhardy nature: It seems foolhardy to me to take potentially provocative and dangerous actions in the service of murky ethics.
I am open to correction.