GUANTANAMO BAY NAVAL BASE, Cuba - An effort to prosecute the self-proclaimed mastermind of the Sept. 11 terrorist attacks and four codefendants veered off track again Thursday as a pretrial hearing ended with new obstacles that threaten to further derail the case before a military tribunal at Guantanamo Bay.

Teams of lawyers managed barely four hours of court time over four days at the U.S. base in Cuba, bogged down by the potential legal implications of an apparent FBI investigation of the defense.

After nearly two years and 10 pretrial sessions, a trial date remains elusive and could be years away. The prosecution had sought to start jury selection early next year, but that now seems impossible amid looming fights over classified evidence from the CIA, among other issues.

The prosecution of Khalid Sheikh Mohammed has already been stalled for years, initially by the U.S. government's decision to hold him in secret detention and later by legal challenges and a fight over whether to try him in civilian or military court.

For observers whose family members were killed in the Sept. 11, 2001, attacks, the pace has been excruciating.

"This week has been difficult because it brings back a lot of emotion," said Gloria Snekszer, an Atlanta-area woman whose sister, Vicki Linn Yancey, was killed on the plane that crashed into the Pentagon. "One of the hardest things for me to deal with was the constant delay, the thought that this may never come to conclusion."

Some family members were so angry about the situation that they walked out of a private meeting Wednesday with defense lawyers intended to help them understand the process. "It is one thing to have a fair trial; it is another to drag it out and drag it out," said Don Arias, a resident of Panama City, Fla., whose brother, Adam, was killed in the World Trade Center.

The five defendants were arraigned in May 2012 on charges that include terrorism and nearly 3,000 counts of murder in violation of the law of war. They have yet to formally enter pleas, but Mohammed has told authorities that he orchestrated the terrorist plot. The other four are accused primarily of providing financial and other logistical support to the hijackers. All could get the death penalty if convicted.

In December, the judge halted progress on pretrial motions because prosecutors wanted to determine the mental competency of defendant Ramzi Binalshibh after his repeated outbursts in court.