The soldiers who guard Khalid Sheikh Mohammed say he is a calculating man, a monster in a monk's habit and a leader of the prisoners locked away in Guantanamo Bay, where he's on trial for the murder of thousands.

With rare access and interviews, FOX News has learned new and sobering details about "The Sheikh," the man known simply as KSM.

"I was there when they read him his charges," said Brig. Gen. Gregory Zanetti, deputy commander of Joint Task Force Guantanamo. "Pretty sobering moment — charged with murder, terrorism, conspiracy. He looked at the sheet and said 'I did this, I did this, I did this. I did more than this. I'm guilty. I feel sorry for my defense attorney.'"

Zanetti told FOX News about life behind the wire at Guantanamo Bay's maximum security camps. Camp 7 is home to the most notorious, including Mohammed, the master planner of 9/11.

"He's very compliant, he is very studious and he is very calculating. He thinks things through very well, he plays things out. When you watch him in court, he has all of this choreographed," Zanetti said.

Including his stated intention, last week, to plead guilty to the 9/11 charges.

"He wants to die — he wants to be a martyr for the cause. He believes his story is being written right now, to be laid down side by side next to [the Prophet] Muhammad," Zanetti told FOX News.

Inside Guantanamo, maximum security cells provide an arrow pointing toward Mecca to orient the prisoners for prayer. Mohammed prays constantly, apparently a devout man, which Zanetti finds mystifying.

"The guy's got a long beard, studious glasses — he looked like a professor. ... You see him in a cell and he'll pray hours on end. What God are you praying to? What are you thinking, what is going on up there?" Zanetti wonders. "But if he could do it all again, he would."

Even in captivity, he still is leading members of Al Qaeda, who fall in lock-step with his plans.

"He knows what he's going to say, the message he wants to get out, what he's going to have his followers do. You've seen him in court — very quickly people fall in behind him."

Sketch artist Janet Hamlin's brush with Mohammed came at his first court appearance at Guantanamo in June. As a courtesy, the military allowed KSM to review the sketch. He quickly sent word to Hamlin that he hated it.

"He doesn't like it. He's saying he won't approve of it, it cannot be released until the nose is changed," she told FOX News. Mohammed made his demands clear: "'Tell her to find my FBI photo off the Internet, use that as reference. Fix it.'"

Mohammed's concern about his image is fundamental, but it can also breed rivalries among the detainees.

"You see this inside the camps; they get jealous of each other: 'You were in the news more than I was in the news.' It drives [Mohammed] crazy if he thinks no one cares. He thinks he's part of this much bigger picture," Zanetti said.

But the picture inside Guantanamo is often an ugly one. Some prisoners do all in their power to violate the guards.

"What they do is stuff that you and I would find despicable. They save up their bodily fluid, feces and so on, and then when the guard comes to deliver food, they get a feces cocktail thrown in their face."

It's something Zanetti says occurs almost daily, and weighs heavily on the guards, who are tasked with feeding and clothing the prisoners and tending to them when they are sick. Hospital staff get the worst exposure of all from the detainees, he said.

"You ensure that their life is as comfortable as possible while the detainees are trying to make the guards' life as miserable as possible."

Those daily doses of hatred are a stark reminder about some of the men locked up inside the camp, including Mohammed, who has claimed responsibility for decapitating Wall Street Journal reporter Daniel Pearl in 2002.

"We have more than our fair share of Hannibal Lecters around here," Zanetti said.