Abstract: THE Obama administration wants to show that federal courts can handle trials of Guantanamo Bay detainees, and had therefore placed high hopes in the prosecution of Ahmed Khalfan Ghailani, accused in the 1998 bombings of American embassies in East Africa. On Wednesday a federal judge, Lewis Kaplan of the United States District Court in Manhattan, made the government's case much harder when he excluded the testimony of the government's central witness because the government learned about the witness through interrogating Mr. Ghailani at a secret overseas prison run by the C.I.A.