GUANTANAMO BAY NAVAL BASE, Cuba — Lawyers for Guantanamo prisoners charged in the Sept. 11, 2001, terrorist attacks say the FBI has questioned more support staff members on their legal teams than previously disclosed, a development that stands to prompt a new detour in an already snarled case as the base’s war crimes tribunal reconvened Monday.

The trial by military commission of the five prisoners was derailed in April when the attorney for one defendant revealed that a member of his support staff was questioned at home by the FBI and asked to provide information on others who work for the defense.

Lawyers say they have since learned that at least three others have been questioned in two separate investigations over the past year. They want a judge to conduct a full hearing with witnesses into the issue.

Lawyers say the FBI questioned an investigator and a classified material analyst for the team representing defendant Ramzi Binalshibh; an investigator for defendant Mustafa al-Hawsawi; and a translator on the team representing Mohammed, who has portrayed himself as the mastermind of the 9/11 attacks.

James Harrington, a lawyer for Binalshibh, told the court his investigator denied speaking to the FBI and has left his team. “We have had basically a spy within our team for a number of months,” he said.