Attorney General Eric Holder this morning defended his decision to try 9/11 “mastermind” Khalid Shaikh Mohammed (often simply referred to by his initials, KSM) and four other suspected terrorists at a New York City federal court. He was testifying before the Senate Judiciary Committee.

Holder announced Friday that he would have federal attorneys from the Southern District of New York and the Eastern District of Virginia prosecute the alleged terrorists in New York and not in a military court. He also said he would have five other suspected terrorists tried before military commissions.

“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 in his prepared opening statement before the Senate panel. “We need not cower in the face of this enemy. Our institutions are strong, our infrastructure is sturdy, our resolve is firm and our people are ready.”

The panel’s ranking Republican, Jeff Sessions of Alabama, said at the hearing that all suspected terrorists should be tried in military courts.

“I believe this decision is dangerous,” Sessions said in his opening statement. “I believe it is misguided. I believe it is unnecessary.”

Holder said his decision was a “tough call” and knew “reasonable people” would disagree with his judgment.

“As I said on Friday, I knew this decision would be controversial,” Holder said.

The Attorney General said terrorists have been “safely and securely” prosecuted in federal courts, and that classified material would be protected. Holder said that KSM would have “no more of a platform to spew his hateful ideology in federal court than he would have in military commissions.”

Holder added that there is “nothing common” about how the government will treat the suspected terrorists and said the Justice Department is not reverting to a “pre-9/11 mentality.” The Attorney General said he will advise the prosecutors to seek the death penalty.

“It is time, it is past time, to act,” Holder said. “By bringing prosecutions in both our courts and military commissions, by seeking the death penalty, by holding these terrorists responsible for their actions, we are finally taking ultimate steps toward justice. That is why I made this decision.”

The Attorney General drew chuckles from the audience when he responded to a question from Sen. Herb Kohl (D-Wis.) about what the Justice Department would do if the suspected terrorists tried in federal court weren’t convicted.

“Failure is not an option,” Holder said. “These are cases that have to be won.” He later clarified his remarks and said the suspected terrorists would not be set free if they weren’t convicted.

Panel Chairman Patrick Leahy (D-Vt.) said he has “great confidence” in the ability of civilian courts to handle the terrorism cases.

“War crimes, crimes of terror, and murder can successfully be prosecuted in our federal courts, as we have demonstrated time and again,” Leahy said in his opening statement. “America’s response to these acts is not to cower in fear, but to show the world that we are strong, resilient and determined.”

This post has been updated from an earlier version.