WASHINGTON - The alleged mastermind behind the September 11 attacks and four other suspects appeared in a U.S. military tribunal at Guantanamo Bay Saturday morning.

The arraignment marks the second time the United States has tried to prosecute the 9/11 suspects. Khalid Sheikh Mohammed and his four codefendants have not been seen in courtroom for about three years. They have been held in a classified section of Guantanamo under tight security.

Khalid Sheikh Mohammed is accused of obtaining approval and funding from bin Laden for the attacks, overseeing the entire operation and training the hijackers in all aspects of the operation in Afghanistan and Pakistan.

The overall charges allege that the five accused are responsible for the planning and execution of the attacks of September 11, 2001, resulting in the killing of 2,976 people. If convicted, they could get death penalty.

About a dozen of family members of the September 11 attacks victims and nearly 60 media representatives are allowed to the naval station in Guantanamo Bay to watch the proceedings, the Pentagon said.

The Pentagon said the defendants have been provided counsel with specialized knowledge and experience in death penalty cases in a bid to assist them in their defense.

The Pentagon has arranged several viewing sites based in the United States to show the proceedings to victims' families and members of the media by closed-circuit TV. Some 400 to 600 first responders to the 9/11 terror attack sites will also watch the commission proceedings for the first time at view sites.

The administration announced in November 2009 that Khalid Sheikh Mohammed would be tried in a court near the World Trade Center.

In December 2010, the Congress adopted restrictions on prosecuting Guantanamo prisoners in civilian courts. The five suspects were referred to the Pentagon in April 2011, for trials in military tribunals. Officials have said the administration still aims to close the Guantanamo prison facility despite the policy about-face.

Obama promised to shut the Guantanamo Bay prison facility within one year since he took office, but has not succeeded in doing so.

The detention camp is the epicenter of controversial detainment and interrogation practices used by the United States in its war against terror, as detainees were held indefinitely without charges and subjected to harsh interrogation methods such as water-boarding.