Shahzad, 30, said "he wanted ‘to plead guilty and 100 times more’ to let the US know that if it did not get out of Iraq and Afghanistan, halt drone attacks and stop meddling in Muslim lands, 'we will be attacking the US.'"
The Pakistani-born US citizen tried to set off a car bomb in New York's Times Square on May 1 but street vendors spotted the smoking vehicle almost immediately and notified the New York Police Department, which cleared the area.
After firefighters doused the flames, the search began for whoever had left the vehicle. It was quickly traced to Shahzad.
Although federal guidelines indicate a life sentence for Shahzad, it might depend on what prosecutors told him to get him to cooperate, officials say.
"The devil is in the details," said a former prosecutor anonymously. "But no matter what, he will get a significant sentence. You don't want to send the message that if you tried to kill hundreds, if not more, but got caught and cooperated, you don't get so much jail time."
Shahzad's admission of guilt had been expected. He waived his right to a speedy arraignment, and he gave the US government information about his training and contacts in Waziristan, Pakistan, with explosives trainers.
Observers say what was not expected was the defiance with which Shahzad defended what he did.
Shahzad told US District Judge Miriam Goldman Cedarbaum he was "a Muslim soldier" avenging the deaths of Muslims killed by Americans overseas, and that he didn't care that his bomb could have killed children.
"It's a war. I am part of the answer to the US terrorizing the Muslim nations and the Muslim people," he said.
"One has to understand where I'm coming from," Shahzad told the judge, who challenged him with questions such as whether he had qualms about killing children in Times Square.
"It's a war," he said.
He described his effort to set off a bomb in an SUV he parked in Times Square on May 1, saying he chose the warm Saturday night expecting that would bring out a big crowd.
He said he conspired with the Pakistani Taleban, which provided more than $16,000 to fund his operation and five days of explosives training late last year and early this year, just months after he became a US citizen.
Federal authorities have said they believe money was channeled through an underground money-transfer network known as hawala.
Shahzad explained that he actually packed his vehicle with three bombs, hoping to set off a fertilizer-fueled bomb packed in a gun cabinet, a set of propane tanks, and gas canisters rigged with fireworks to explode into a fireball.
He said he had expected the bombs to begin going off after he lit a fuse and waited between 2-1/2 and 5 minutes for them to erupt.
"I was waiting to hear a sound, but I didn't hear a sound," he said. "So I walked to Grand Central and went home." He insisted he built the bombs "all by myself."
Shahzad dismissed the judge's question about potentially harming children by saying the United States did not care when children were killed in Muslim countries.
"It's a war. I am part of the answer to the US terrorizing the Muslim nations and the Muslim people. On behalf of that, I'm revenging the attack. Living in the United States, Americans only care about their people, but they don't care about the people elsewhere in the world when they die."
Cedarbaum asked Shahzad if he understood that the people in Times Square might not have anything to do with what happened overseas.
"The people select the government," Shahzad said. "We consider them all the same."
Three men in Massachusetts and Maine suspected of supplying money to Shahzad are being held on immigration charges.
He faces life in prison when he is sentenced on Oct. 5. He is likely to end up in a federal penitentiary either in Florence, Colo., or in Terre Haute, Ind. The worst of the worst are sent to Colorado's "administrative maximum" prison, known as Supermax.
Ramzi Yousef, the 1993 World Trade Center bomber, renounced Islam there. Other inmates are Unabomber Ted Kaczynski and Al-Qaeda heavyweight Zacarias Moussaoui.
