GUANTÁNAMO BAY, Cuba — The military judge presiding in the trial of five men accused of plotting the Sept. 11, 2001, terrorist attacks announced in court on Wednesday that he intends to leave the case next month.
The development could further delay the slowly moving case as a new judge reads the more than 23,000 pages of pretrial transcripts dating back to the May 2012 arraignment as well as hundreds of pretrial pleadings.
The announcement came just days after the commander of the prison at Guantánamo Bay, Rear Adm. John C. Ring, was fired after a monthlong investigation, for what his superior officer called a “loss of confidence in his ability” to lead.
The current judge, Col. Keith A. Parrella of the Marines, took over the case a little more than eight months ago. He said he was leaving for a job supervising Marine security forces at United States embassies around the world, a possibility he had flagged when he held his first hearing in the case last September. No replacement was named for him.
Colonel Parrella replaced the case’s long-serving judge, Col. James L. Pohl of the Army, who handled the complex capital conspiracy case against Khalid Shaikh Mohammed and four other former C.I.A. prisoners for the first six years before retiring.
Mr. Mohammed and the others are accused of directing, training or assisting the 19 men who hijacked passenger planes on Sept. 11, and then crashed them into the World Trade Center, the Pentagon and a Pennsylvania field, killing 2,976 people. No trial date has been set.
Colleen J. Kelly, a nurse practitioner from the Bronx whose brother, William Kelly Jr., was killed in the attack on the World Trade Center declared herself “shocked” and “deflated” by the change in judges, which she called “disrespectful.”
Ms. Kelly has been following the proceedings as a member of the group Sept. 11 Families for Peaceful Tomorrows. She said that the need for a new judge underscores why the case should be tried in federal courts, which Congress has forbidden. “It could be done in two years,” she predicted.
At Guantánamo, however, “this thing is going to die from neglect,” Ms. Kelly said. “Or the prisoners first and, ultimately, maybe that’s the strategy, which seems a pretty anemic justice to me.”
This week was the fifth time that Colonel Parrella had traveled to Guantánamo to preside in weeklong pretrial hearings before seating a jury of military officers.
Colonel Parrella had scheduled two key hearings that will now be left to his successor.
In one, he had planned to hear testimony from a former C.I.A. black site interpreter in closed court. But the war court’s appeals panel, the United States Court of Military Commission Review, blocked the testimony while it considers whether the public and the defendants are entitled to listen to unclassified portions.
Colonel Parrella also ordered a hearing on the question of the admissibility at trial of confessions Mr. Mohammed and the others allegedly gave to F.B.I. agents soon after their 2006 transfer to Guantánamo from the C.I.A.’s secret prison network.
The first judge in the case had forbidden their use because prosecutors limited the evidence defense lawyers could have access to and prohibited them from trying to interview most former black-site workers — restrictions that he found hamstrung defense investigations and the detainees’ right to a fair trial.
Colonel Parrella, however, decided to test the defense lawyers’ ability to challenge the F.B.I.’s so-called clean team interviews. He ordered prosecutors and defense lawyers to present briefs on the question by May 10, including a proposed list of witnesses, some of whose identities are not known to the lawyers.
The judge’s announcement Wednesday made clear that he intended to leave that complex hearing to his successor.
It was not immediately clear when Colonel Parrella would stop deciding motions in the case. But he said on Wednesday, at the end of his last open hearing of the week, that he intended to report to his new job as commander of the Marine Corps Embassy Security Group in Quantico, Va., in early June.
The military commission’s court calendar has blocked out the week of June 17 for the next pretrial hearing, after the court’s customary monthlong recess for Islam’s holy month of Ramadan.