Washington (CNN) - Attorney General Eric Holder defended his decision Wednesday to try five suspected 9/11 terrorists in civilian court.
"We are at war and we will use every instrument of national power - civilian, military, law enforcement, intelligence, diplomatic and others –to win," he told members of the Senate Judiciary Committee. "We need not cower in the face of this enemy. Our institutions are strong."
Holder announced last week that the suspected terrorists - including confessed 9/11 mastermind Khalid Sheikh Mohammed - will be tried in civilian court in New York City.
All five suspects have been held in the U.S. detention facility at Guantanamo Bay, Cuba. Critics of Holder's decision have argued that the suspects should be tried by a military tribunal.
"There is nothing common about the treatment the alleged 9/11 conspirators will receive," Holder promised. "In fact, I expect to direct prosecutors to seek the ultimate and most uncommon penalty for these heinous crimes."
The attorney general has promised to seek the death penalty for all five suspects.
Vermont Sen. Patrick Leahy, the chairman of the Judiciary Committee, said at the start of the hearing that he agrees with Holder's decision.
The alleged terrorists "should answer for their brutality," he said. "I have full confidence in the capacity of New York" to try the case.
Federal courts have successfully tried over 100 terrorist cases since the September 11 attacks, he said.
Alabama Sen. Jeff Sessions, R-Alabama, questioned Holder's judgment. Sessions argued the decision to try the five suspects in a civilian court was one of many Obama administration actions signaling to allies that "fighting global terrorism is not the priority it once was."
Holder said he knows "we are at war with a vicious enemy who targets our soldiers on the battlefield in Afghanistan and our civilians on the streets here at home. ... Those who suggest otherwise are simply wrong."
Dozens of family members of 9/11 victims recently signed a letter to Holder and President Barack Obama opposing a civilian trial for the alleged plotters.
They said it would give the men a well-publicized platform to espouse their views, in a trial to be held just blocks from where the World Trade Center towers crumbled when the hijacked planes crashed into them.
"Khalid Sheikh Mohammed will have no more of a platform to spew his hateful ideology in federal court than he would have in military commissions," Holder replied Wednesday.
"Before (his military) commissions last year, he declared the proceedings an 'inquisition,' condemned his own attorneys and our Constitution, and professed his desire to become a martyr. Those proceedings were heavily covered in the media, yet few complained at the time that his rants threatened the fabric of our democracy."
Holder brushed aside concerns that the suspects might be found innocent by a federal court. He said he has told prosecutors that "failure is not an option. ... These are cases that have to be won."
His decision, he said, "will withstand the judgment of history."