Separately on Thursday, Colonel Pohl ordered the Pentagon official in charge of the tribunals — Vice Adm. Bruce MacDonald, retired — to testify at a hearing next month. Defense lawyers are seeking to scuttle the charges and reboot the case, asserting that his original decision to refer the capital charges to the tribunal was flawed.

One of several relatives of victims who traveled to Guantánamo to watch the hearing, Phyllis Rodriguez, whose son Gregory Rodriguez was killed at the World Trade Center, said she was disturbed by the limits on the openness of the proceedings and difficulties that defense lawyers had in gathering information that could mitigate against death sentences. Ms. Rodriquez said she opposed death sentences on principle and was opposed to prosecuting the case in a tribunal.

But Matthew Sellitto, whose son — also named Matthew — was also killed in the attacks, called the process fair, saying the defendants would have already been executed by now in most countries. His wife, Loreen Sellitto, urged defense lawyers not to delay the proceedings, while describing the emotional experience of seeing the defendants in the courtroom.

“I didn’t expect them to look normal and have normal faces,” Ms. Sellitto said. “That scared me.”

In a related development, the Pentagon disclosed that earlier this week, Admiral MacDonald withdrew tribunal charges against three other detainees at Guantánamo. Accused of conspiracy and of providing material support to terrorism in connection with accusations related to explosives training, the three were among those arrested in a March 2002 raid in Pakistan that also captured a more prominent terrorism suspect, Abu Zubaydah.

The validity of bringing charges of material support and conspiracy in a tribunal — at least for actions before October 2006, when Congress approved them as triable offenses in a military commission — has been a point of sharp contention inside the Obama administration. A federal appeals court recently vacated two such verdicts from tribunal cases because such offenses were not recognized as international war crimes.