The very first trial under the Military Tribunal system of justice for detainees at Guantanamo could be a capital case involving 6 terrorists charged with complicity in the 9/11 attacks on the United States:

The officials said the charges would be announced at the Pentagon as soon as Monday and were likely to include numerous war-crimes charges against the six men, including Khalid Shaikh Mohammed, the former Qaeda operations chief who has described himself as the mastermind of the attacks, which killed nearly 3,000 people.

A Defense Department official said prosecutors were seeking the death penalty because “if any case warrants it, it would be for individuals who were parties to a crime of that scale.” The officials spoke anonymously because no one in the government was authorized to speak about the case.

A decision to seek the death penalty would increase the international focus on the case and present new challenges to the troubled military commission system that has yet to begin a single trial.

“The system hasn’t been able to handle the less-complicated cases it has been presented with to date,” said David Glazier, a former Navy officer who is a professor at Loyola Law School in Los Angeles.

In addition to Mr. Mohammed, the other five to be charged include detainees officials say were coordinators and intermediaries in the plot, among them a man labeled the “20th hijacker,” who was denied entry to the United States in the month before the attacks.