This article was produced in partnership with the Pulitzer Center on Crisis Reporting.

GUANTÁNAMO BAY, Cuba — A long-serving capital defense lawyer for one of the five men accused of plotting the Sept. 11, 2001, attacks asked the judge on Tuesday to be excused from the case, citing his health and other issues, casting doubt on whether the trial can begin as scheduled next year.

Col. W. Shane Cohen, the judge, recessed what was meant to be a week of pretrial hearings to allow the lawyer, James P. Harrington, to put his request to leave the case in writing. The judge also invited prosecutors and defense lawyers to weigh in on whether the defendant Mr. Harrington represents, Ramzi bin al-Shibh, should be tried separately from the other four.

Prosecutors have consistently sought to put all five defendants on trial together, arguing that multiple trials would be too stressful for the families of the 2,976 victims killed in the attacks.

Mr. bin al-Shibh, a Yemeni, is accused of organizing the Hamburg, Germany, cell of the hijackers and acting as a go-between for the cell and the man accused of being the plot’s mastermind, Khalid Shaikh Mohammed.