Justice Ministry spokeswoman Katharina Jahntz on Saturday confirmed a report in Der Spiegel that a German observer would attend the trial to ensure that no evidence provided by Germany would be used to apply the death penalty.
U.S. authorities announced last week that Khalid Sheikh Mohammed would be tried by a New York court. No date has been set.
Three of the four suicide pilots who carried out the attacks had lived and studied in the northern German city of Hamburg.
Germany, like the rest of Europe, except for Belarus, does not execute criminals.