Khalid Sheikh Mohammed and four other alleged 9/11 plotters have been charged in the US, according to reports on Wednesday.
The suspected terrorist has been in custody in Guantanamo bay over alleged acts of terrorism after being captured in March 2003 in Pakistan.
The US has formally sent the five men, all Guantanamo Bay inmates, to trial. The Pentagon has said they could face the death penalty if convicted.
In a statement the US defence department said: "If convicted, the five accused could be sentenced to death."
All five are charged with "terrorism, hijacking aircraft, conspiracy, murder in violation of the law of war, attacking civilians, attacking civilian objects, intentionally causing serious bodily injury, and destruction of property in violation of the law of war".
"The convening authority has referred all charges to a joint trial," the statement adds.
Khalid Sheikh Mohammed, an alleged Al-Qaeda "king pin", is said to have admitted responsibility for the 9/11 attacks "from A to Z".