GUANTANAMO BAY NAVAL BASE, Cuba — A lawyer for one of five defendants in the Sept. 11 war crimes tribunal said Monday that FBI agents questioned a member of his defense team, apparently in an investigation related to the handling of evidence, a revelation that brought an abrupt halt to proceedings.

Attorney James Harrington told the judge presiding over the case at the Guantanamo Bay naval base that the agents asked about activities of others on his defense team as well as of people working for other defendants.

“Obviously, to say that this is a chilling experience for all of us is a gross understatement,” he told the judge.

Harrington did not mention the nature of the FBI’s questions in court, but said later that his court-appointed security officer was asked about the release in January of writings by the lead defendant in the case, Khalid Sheikh Mohammed, to two media outlets.

The defense security officer, a private contractor who assists with the handling of classified material in the death-penalty terrorism trial, was also asked to sign an agreement that implied he might be asked to provide information to the FBI on an ongoing basis in the future, Harrington said. The questioning occurred April 6 at the man’s home in the United States, not on the U.S. base in Cuba.

After the FBI visit, the contractor informed his employer, SRA International Inc., based in Fairfax, Virginia.

The disclosure came at the start of what was supposed to be a mental competency hearing for Harrington’s client, Ramzi Binalshibh, a Yemeni accused of providing logistical support to the Sept. 11, 2001, terrorist plot. The lawyer said the apparent investigation of defense team members will require review by the court, and possibly the appointment of additional counsel for the defendants because it has created a potential conflict of interest for the attorneys.

“If we are the subject of some inquiry or investigation or whatever by the FBI or some other government agency, then we have an interest in how that comes out and the question becomes whose interest do we protect first, ours or our clients,” he said.

The FBI declined to comment.

Army Brig. Gen. Mark Martins, the chief prosecutor for the Guantanamo tribunals, said the prosecution was not aware of the questioning by the FBI until being informed by the defense. He urged the judge to continue with the scheduled competency hearing, which had already delayed the long-stalled trial by military commission for five Guantanamo prisoners charged with planning and aiding the Sept. 11 terrorist attack.

The judge, Army Col. James Pohl, did not say how he would handle the defense request to put proceedings on hold. He abruptly adjourned for a closed session called by the prosecution to discuss another matter and said court would reconvene Tuesday.

Prosecutors earlier were seeking to determine how a document written by Khalid Sheikh Mohammed, who has portrayed himself as the mastermind of the Sept. 11 attack and other plots, was published in January by Britain’s Channel 4 News and The Huffington Post without apparently going through the normal security screening process.

The document, a 36-page section of a self-styled manifesto by the accused terrorist, was not classified and had been distributed to all the defense teams. Prosecutors have said in court papers that they believe the distribution violated a judge’s order relating to the handling of documents in the case.

Harrington said neither he nor anyone on his team, as far as he knows, released the document. He said he suspects the FBI investigation could be meant as a warning to the lawyers in the Sept. 11 case that they are being scrutinized. “I’m sure there are people in the government that are upset that this thing came out, whether it was legal or not,” Harrington said.

A Defense Department spokesman, Army Lt. Col. Todd Breasseale, said the prosecution in the case has not alleged any misconduct on the part of the defense related to the release of the Mohammed document.

Mohammed and his four co-defendants face charges that include terrorism and nearly 3,000 counts of murder in violation of the law of war and could get the death penalty if convicted. A trial date has not been set.