DETROIT (AP) — A Nigerian man pleaded guilty Wednesday to attempting to bring down an international flight over Detroit with a bomb in his underwear, telling a surprised courtroom on the second day of his trial that the failed attack was retaliation for the killing of Muslims worldwide.

Umar Farouk Abdulmutallab, who had never denied the accusations against him, calmly answered questions from U.S. District Judge Nancy Edmunds before pleading guilty on the second day of his trial to all eight charges he faced, including conspiracy to commit terrorism and attempted use of a weapon of mass destruction.

He then told the court that the underwear bomb was a “blessed weapon to save the lives of innocent Muslims.”

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“The United States should be warned that if they continue to persist and promote the blasphemy of Mohammed and the prophets … the United States should await a great calamity that will befall them through the hands of the mujahedeen soon,” said Abdulmutallab, who faces a mandatory sentence of life in prison.

“If you laugh with us now we will laugh with you later on the day of judgment,” he said.

Outside court, defense attorney Anthony Chambers said Abdulmutallab, who had chosen to represent himself and was being assisted by Chambers, pleaded guilty against the lawyer’s wishes.

“We wanted to continue the trial but we respect his decision,” Chambers said.

Abdulmutallab, 25, said he carried a bomb in his underwear onto Northwest Airlines Flight 253 on Christmas 2009 with the intention of killing the nearly 300 people on board. The bomb didn’t work, and passengers jumped on Abdulmutallab when they saw smoke and fire.

The evidence was stacked high. Abdulmutallab was badly burned on a plane full of witnesses. The government said he told FBI agents he was working for al-Qaida and directed by Anwar al-Awlaki, a radical, American-born Muslim cleric recently killed by the U.S. in Yemen. There were also photos of his scorched shorts as well as video of Abdulmutallab explaining his suicide mission before departing for the U.S.

In September 2010, Abdulmutallab suggested he wanted to plead guilty to some charges. But he didn’t, and instead dropped his four-lawyer, publicly financed defense team and decided to represent himself. He said relying on others wasn’t in his best interest.

His lawyers at the time said they had talked to prosecutors about a possible plea deal. Abdulmutallab had asked the judge what he needed to do to plead guilty to some charges but nothing happened and a trial was set.

“Contrary to what some have claimed, today’s plea removes any doubt that our courts are one of the most effective tools we have to fight terrorism and keep the American people safe,” U.S. Attorney General Eric Holder said in a Wednesday statement. “We will continue to be aggressive in our fight against terrorism and those who target us, and we will let results, not rhetoric, guide our actions.”

Passenger Lori Haskell, 34, of Newport, Mich., watched Abdulmutallab’s plea by video in an overflow room Wednesday. She called his statement in court “chilling” but not surprising.

“I’m just really relieved that it’s done with,” Haskell said.

Abdulmutallab had written a few court filings in his own hand, including a request to be judged by Islamic law. He at times appeared agitated in court, declaring that Osama bin Laden and al-Awlaki are alive. He also objected to trial testimony from experts who would have discussed al-Qaida and martyrdom.

On Tuesday, a passenger on Flight 253 testified that Abdulmutallab took a long bathroom break in the plane, during which prosecutors say he was preparing for death.

“I thought he was freshening up for arrival in Detroit. … We had less than an hour to go,” said passenger Mike Zantow of Madison, Wis.

Assistant U.S. Attorney Jonathan Tukel said the son of a wealthy Nigerian banker believed his calling that day was martyrdom.

“He was preparing to die and enter heaven,” Tukel said. “He purified himself. He washed. He brushed his teeth. He put on perfume.”

After returning to his seat, Abdulmutallab pushed a syringe plunger into the chemical bomb, an action that produced a loud “pop” sound, then flames and smoke, the prosecutor said.

“Then all hell broke loose. While the fireball was on him, the defendant sat there. He didn’t move. He was expressionless. He was completely blank,” Tukel said.

The government says Abdulmutallab willingly explained the plot twice, first to U.S. border officers who took him off the plane and then in more detail to FBI agents who interviewed him at a hospital for 50 minutes, following treatment for serious burns to his groin.

Abdulmutallab told authorities he trained in Yemen, home base for Al-Qaida in the Arabian Peninsula, and was influenced by al-Awlaki, who was killed in a Sept. 30 U.S. military air strike.

Following the strike, a U.S. official outlined new details of al-Awlaki’s involvement against the U.S., including Abdulmutallab’s mission. The official, who spoke on condition of anonymity to discuss intelligence matters, said al-Awlaki specifically directed Abdulmutallab to detonate an explosive device over U.S. airspace to maximize casualties.

Officials have said al-Awlaki was believed to be at a gathering of al-Qaida figures in Yemen’s Shabwa mountains a day before the attack, after which bin Laden appeared in a video declaring Abdulmutallab a “hero.” Abdulmutallab also has been lauded by al-Qaida’s English-language Web magazine Inspire, whose editor was killed along with al-Awlaki.

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Associated Press writers David Runk in Detroit and Matt Apuzzo in Washington contributed to this report.

Copyright 2011 The Associated Press.