GUANTANAMO BAY NAVAL BASE, Cuba >> Prosecutors and defense lawyers began arguing challenges today to holding the trial for five men charged in the Sept. 11 attacks before a military commission at Guantanamo Bay.

Lawyers for the five prisoners charged in the attacks have filed a series of motions seeking to declare that the commission, a hybrid civilian-military court for wartime offenses, unconstitutional. They began arguing them on the fourth day of a weeklong pretrial hearing.

The defense says the war crimes commissions deprive the defendants of some of the rights they would have in a civilian court or military court martial because they are not U.S. citizens. It says the commission system is legally flawed because the Pentagon legal official who presides over the court, known as the convening authority, acts in some ways both as judge and prosecutor.

Defense lawyers also argue that the government cannot make a special category of war crimes just for non-citizens of the United States.

The chief prosecutor, Army Brig. Gen. Mark Martins, defended the commissions, saying the system has “robust” legal protections for the accused and is particularly suited to complex war crimes committed by people outside the U.S.

The United States has used military commissions since the Revolutionary War, but the system was given an overhaul by Congress in 2009 for the tribunals at Guantanamo.

The judge was expected to hear additional arguments and was not expected to issue immediate rulings.

The five prisoners faces charges that include terrorism and murder for their alleged roles planning and aiding the Sept. 11, 2001, terrorist attacks in the United States. They could get the death penalty if convicted.