Even if a terror trial suspect were acquitted, Holder said, he would not be released in the United States.
In one of a series of TV interviews during his trip to Asia, Obama said those offended by the legal privileges given to Mohammed by virtue of getting a civilian trial rather than a military tribunal won't find it "offensive at all when he's convicted and when the death penalty is applied to him."
Obama quickly added that he did not mean to suggest he was prejudging the outcome of Mohammed's trial. "I'm not going to be in that courtroom," he said. "That's the job of the prosecutors, the judge and the jury."
In interviews broadcast on NBC and CNN Wednesday, the president also said that experienced prosecutors in the case who specialize in terrorism have offered assurances that "we'll convict this person with the evidence they've got, going through our system."
Holder sought to explain his prosecutorial strategy Wednesday to the Senate Judiciary Committee, where lawmakers questioned him along largely partisan lines over his decision last week to send Mohammed and four alleged henchmen from a detention center at Guantanamo Bay to New York to face a civilian federal trial in New York.
Asked what might happen if the suspects are acquitted, Holder replied: "Failure is not an option. These are cases that have to be won. I don't expect that we will have a contrary result."
Sen. Charles Grassley pounced on that answer.
"It just seemed to me ludicrous, but I'm a farmer, not a lawyer," Grassley said.
Seeking to allay such concerns, Holder insisted the suspects will be convicted, but even if one isn't, "that doesn't mean that person would be released into our country."
Critics of Holder's decision -- mostly Republicans -- have argued the trial will give Mohammed a world stage to spout hateful rhetoric.
Holder said such concerns are misplaced, because judges can control unruly defendants and any pronouncements by Mohammed would only make him look worse.
"I have every confidence that the nation and the world will see him for the coward that he is," Holder told the committee. "I'm not scared of what Khalid Sheik Mohammed has to say at trial -- and no one else needs to be either."
Holder said the public and the nation's intelligence secrets can be protected during a public trial in civilian court.
"We need not cower in the face of this enemy," Holder says. "Our institutions are strong, our infrastructure is sturdy, our resolve is firm, and our people are ready."
Sen. Patrick Leahy, D-Vt., the committee chairman, supported Holder's decision.
Mohammed, Leahy said, "committed crimes of murder in our country and we will prosecute them in our country. We're the most powerful nation on earth, we have a justice system that is the envy of the world. We will not be afraid."
Tempers flared when Sen. Jon Kyl, R-Ariz., challenged Holder to say how a civilian trial could be better, since Mohammed has sought to plead guilty to a military commission.
"How could he be more likely to get a conviction than that?"
pressed Kyl, to applause from some in the hearing room.
The attorney general said his decision is not based "on the whims or the desires of Khalid Sheikh Mohammed ... He will not select the prosecution venue, I will. And I have."
The transfer of suspects to New York is still many weeks away.
Geraldine Davie, whose 23-year-old daughter died at the World Trade Center's Tower One, attended the hearing as a spectator, and said she wants Mohammed to stay in the military system. "He's not a U.S. citizen, why should he have those rights? My daughter didn't have those rights," said Davie, who lives in Springfield, Va.
Opponents of the plan, including Holder's predecessor Michael Mukasey, have accused him of adopting a "pre-9/11" approach to terrorism.
Holder emphatically denied that.
"We are at war, and we will use every instrument of national power -- civilian, military, law enforcement, intelligence, diplomatic and others -- to win," Holder said.
