Sitting on the front row of a war court on the US’s Guantanamo Bay naval base in Cuba, Khalid Sheikh Mohammed, one of the world’s most notorious defendants, appeared to listen intently.

“Can you confirm that Mr Mohammed is pleading guilty to all charges and specifications without exceptions or substitutions?” the judge asked his lawyer as Mohammed watched on.

“Yes, we can, Your Honour,” the lawyer responded.

Sitting in court, 59-year-old Mohammed, his beard dyed bright orange and wearing a headdress, tunic and trousers, bore little resemblance to a photo circulated shortly after his capture in 2003.

Mohammed, the accused mastermind of the 9/11 terror attacks on the US, had been due to plead guilty this week – more than 23 years after almost 3,000 people were killed in what the US government has described as “the most egregious criminal act on American soil in modern history”.

But two days later, just as Mohammed had been set to formally enter his decision – the product of a controversial deal he struck with US government prosecutors – he instead watched silently as the judge said the proceedings had been paused under the orders of a federal appeals court.

It was expected to be a landmark week for a case that has faced a decade of delays. Now, with a new complication, it continues into an uncertain future.

“It’s going to be the forever trial,” the relative of one of the 9/11 victims said.