A military judge has excluded a key confession from Khalid Sheikh Mohammed, the self-proclaimed mastermind of the September 11, 2001 attacks, in a ruling that could significantly delay or derail the case. The decision by trial judge Lt. Col. Michael Schrama found that statements made by Mohammed to investigators in 2007 were not voluntarily given.

The ruling, which was not immediately made public due to a security review, comes just days after Schrama scheduled Mohammed's trial for June 2028. The 25th anniversary of the attacks, which killed nearly 3,000 people, is approaching in two weeks.

Rear Adm. Aaron C. Rugh, the top military prosecutor on the case, told The New York Times that he would review the ruling and decide in the near future whether to appeal. An appeal could further prolong the legal proceedings, raising concerns among victims' families that Mohammed might die before being convicted.

Mohammed was captured in Pakistan in March 2003 and has been held at the U.S. detention facility in Guantanamo Bay, Cuba. The legal process for him and other defendants in the 9/11 case has been marked by numerous delays and legal challenges over the years.