Supposedly for being the “20th 9/11 Hijacker.” However, two attempts to charge him failed due to the admission by the United States that he was tortured for information. It is pretty much impossible to try him as the case against him is totally compromised by misbehavior by the United States Government. And even if that wasn’t the case, his current mental condition makes it very likely any attempt to prosecute him would fail due to his mental state.