Critics say it has become one of the biggest failures of the war on terrorism.
Global search for al-Qaeda's No. 3 leader took 18 months
The 21st anniversary of the terrorist attacks is drawing near on Sunday.
Mohammed and four others accused of crimes related to 9/11 are still in a US custody in Guantanamo Bay
His planned trial before a military tribunal has been adjourned endlessly.
Relatives of the nearly 3,000 victims of the attack have long hoped the trial will close