DETROIT — Umar Farouk Abdulmutallab, the man accused of trying to blow up Northwest Flight 253 on Christmas Day 2009 with a bomb in his underpants, sat expressionless as shocked passengers shouted at him, “Your pants are on fire,” according to testimony today, the first day of the trial of the so-called Underwear Bomber.

Assistant U.S. Attorney Jonathan Tuckel described Abdulmattab as an alleged al Qaeda member who calmly attempted to blow up the plane and then sat expressionless while his underwear burned because he had fully accepted his mission of martyrdom.

“His mission, his goal, was to blow it up,” Tuckel said during his opening statement at the trial in U.S. District Court. “It had to be blown up over U.S. soil.”

Abdulmutallab made numerous trips to the bathroom and prayed and went through rituals before allegedly depressing a plunger on a syringe, setting off a chemical reaction of two high explosives, Tuckel said.

“There was a loud pop … smoke … a fireball … the fireball was on the defendant … he was engulfed,” the prosecutor said.

Michael Zantow a passenger aboard the flight who was seated one row away from Abdulmutallab said people were alarmed by the initial loud pop of the device. He said someone yelled, “Hey man, hey dude, your pants are on fire.”

“This guy’s pants is on fire,” another passenger yelled, according to Zantow.

Zantow said that passengers struggled to get Abdulmutallab’s seatbelt off and lifted him out of his seat and laid him down on the floor with his pants down to his knees and the device smoldering.

“It was bulky and they were burning,” Zantow said. “It looked like my son’s Pampers.”

Zantow echoed Tuckel’s statement in his opening arguments that Abdulmutallab sat expressionless as he was enveloped by the flames.

“I never saw any reaction at all,” Zantow said about the 24-year-old Nigerian who faces terrorism charges for the attempted bombing and conspiracy allegedly organized by Al Qaeda.

Abdulmutallab, whose handcuff were removed before the jury was seated,  sat quietly watching the proceedings wearing a gray and yellow dashiki and a skullcap.

Tuckel described how passengers were unable to put out the chemical fire that had engulfed Abdulmutallab and that flight attendants had to use fire extinguishers on him. As the crew fought the fire, one flight attendant notified the pilots.

“We need immediate assistance.” co-pilot Steve Stewart told air traffic controllers according to tapes played in the court.

The jury heard how controllers cleared the airspace for an emergency landing as the plane descended almost 3,000 feet in 60 seconds. The jury heard the radio communications from the flight with Stewart asking for fire trucks and the authorities.

“We have found out there was some firecrackers that went off,” Stewart said on the audio tapes. “We have him subdued we need the authorities.”

After the fire was contained, Abdulmutallab was brought up to a business class seat where an airline employee and flight attendant watched him while he sat with no pants and a blanket wrapped around him, prosecutors said.

Only seven minutes passed from the time the explosive device went off till the flight landed in Detroit, according to a timeline with the elevation and route of the plane.

Tuckel said that on numerous occasions after he was removed from the aircraft, Abdulmutallab told federal agents and medical workers it was his intention to bring the plane down and that he was a member of al Qaeda.

He allegedly told Customs and Border Protection officer Marvin Steigerwald that he obtained the device in Yemen and that he hid it in his underwear. When he was questioned later by two FBI agents, Abdulmutallab allegedly said he went to Yemen to become involved in jihad and that he was influenced by a man named Abu Tarak to undertake a suicide operation.

When he was taken to the hospital for his severe burns Abdulmutallab told a nurse that he intended to kill himself aboard the aircraft.

Abdulmutallab’s stand-by counsel Anthony Chambers tried today to prevent pictures of burns on Abdulmutallab’s genitals and legs from being entered into evidence, but U.S. District Judge Nancy Edmunds denied the request.

Abdulmutallab came from a privileged family in Nigeria and that he studied abroad in London and Dubai but then became influenced by the radical cleric Anwar Al-Awlaki.

“He had the opportunity to do anything he wanted in life,” Tuckel said. “He wanted jihad and he sought it out.”

The jury saw still images from Abdulmutallab’s martyrdom video that was later released by al Qaeda in the Arabian Peninsula after the failed bombing attack. Tuckel said the jury would see evidence including fingerprints recovered from the remnants of the bomb and an encryption code that Abdulmutallab had kept in his shoe allegedly to communicate with al Qaeda members on computers.

Following Tuckel’s opening statement, Chamber’s reserved the right to give an opening argument later and the trial proceeded with witness testimony. The prosecution is expected to call several passengers as witnesses from the flight in the next day. Later the jury will hear from expert witnesses on al Qaeda and martyrdom.

The jury will also see a video showing the destructive force a model of Abdulmutallab’s underwear bomb could have had on the aircraft’s aluminum skin.  The government intends to call an explosives expert who will address why the device failed to detonate despite allegedly having almost 200 grams of the high-explosives triacetone triperoxide and pentaerythritol tetranitrate.