Holder said he had elected to forgo military trials and instead to proceed with the first U.S. criminal prosecution of figures alleged to have been directly involved in the suicide hijacking plot eight years ago that targeted the World Trade Center and the Pentagon because of his full confidence in a "successful outcome."

He said he expected to ask for the death penalty.

Americans, especially families of the 2,872 people who were killed on Sept. 11, 2001, "deserve the opportunity to see the alleged plotters of those attacks held accountable in court, an opportunity that has been too long delayed," he told reporters.

The case will force the court to confront a host of tough issues, including rough treatment of detainees, intelligence disclosures, and the potential spectacle of terrorists disrupting proceedings. U.S. civilian courts prohibit evidence obtained through coercion, and a number of detainees were questioned using harsh methods some call torture.

Civil rights groups hailed the decision; Republican critics and others decried it. Administration officials said the decision was a "significant step" toward fulfilling President Obama's campaign promise to close the detention center at the U.S. naval base in Guantanamo Bay, Cuba.

"The transfer of these cases is a huge victory for restoring due process and the rule of law, as well as repairing America's international standing," said Anthony D. Romero, executive director of the ACLU.

Congressional Republicans accused the Obama administration of returning to a pre-Sept. 11 mentality of responding to terrorism as if it were criminal activity rather than a war on the United States.

House Republican leader John A. Boehner of Ohio said the possibility that the accused terrorists "could be found not guilty due to some legal technicality just blocks from ground zero should give every American pause."

Pentagon and Justice Department officials said privately that in the unlikely event of an acquittal, authorities would have the ability not to release a defendant into the U.S. population.

Family members of Sept. 11 victims also were divided.

"We have a president who doesn't know we're at war," said Debra Burlingame, whose brother, Charles Burlingame, was the pilot of the hijacked plane that crashed into the Pentagon. She said she was sickened by "the prospect of these barbarians being turned into victims by their attorneys."

Valerie Lucznikowska, whose nephew died at the World Trade Center, said she wouldn't care if the suspects sounded off in court - as long as the victims' families got to see them put on trial.

"What are words? It was a horrible thing to have 3,000 people killed," she said.

New York Mayor Michael Bloomberg said he spoke to Holder and supported holding the trials in his city.

Holder said he had decided that five other Guantanamo detainees would stand trial before military commissions, including Abd al-Rahim al-Nashiri, who is accused of orchestrating the October 2007 attack on the USS Cole in Yemen that killed 17 U.S. sailors and injured 39 others.

"To the extent that there are political consequences, I'll just have to take my lumps," he said.

He said he decided to bring Mohammed and the other four before a civilian court rather than a military commission because of the nature of the undisclosed evidence against them, because the 9/11 victims were mostly civilians, and because the attacks took place on U.S. soil.

"I will say that I have access to information that has not been publicly released that gives me great confidence that we will be successful in federal court," he said.

He said a grand jury indictment soon would be returned against Mohammed, who has admitted to spearheading the planning; Ramzi Binalshibh; Waleed bin Attash; Mustafa Ahmad al-Hawsawi; and Ali Abd al-Aziz Ali.

All five have been held for years at Guantanamo Bay.

Asked about the decision at a Tokyo news conference, Obama said: "I am absolutely convinced that Khalid Sheikh Mohammed will be subject to the most exacting demands of justice."

Democratic Sen. Patrick Leahy of Vermont, chairman of the Senate Judiciary Committee, praised Holder's decision, saying that federal courts have proved "time and time again" they're "capable of trying high-profile terrorism and national security cases."

Kirk Lippold, former commander of the USS Cole, who is now a senior military fellow at Military Families United, praised the decision to refer for military trials alleged mastermind Abd al-Rahim al-Nashiri and four others suspected of attacking the ship.

"It is certainly a step in the right direction for the Obama administration to at last recognize the value and legitimacy of military commissions in dealing with the remaining . . . detainees," he said.

The Justice Department later said the four defendants, in addition to Nashiri, who are to be tried before military commissions are Ahmed Mohammed Ahmed Haza al-Darbi, Noor Uthman Mohammed, Ibrahim Ahmed Mahmoud al-Qosi and Omar Ahmed Khadr.