A man accused of helping to build a truck bomb used in a 1998 terror attack on a U.S. embassy was a member of an al-Qaida cell that was determined to kill Americans, a federal prosecutor told jurors Tuesday, but a defense lawyer said the Tanzanian man was duped.

Assistant U.S. Attorney Nicholas Lewin said in his opening statement Tuesday that Ahmed Khalfan Ghailani — the first Guantanamo Bay detainee to face a civilian trial — bought the truck and gas tanks that were used in the bombing in Tanzania, one of two simultaneous embassy bombings in Africa that killed 224 people, including a dozen Americans.

"This man, Ahmed Ghailani, was a vital member of that cell," Lewin said as he pointed at Ghailani, who stared straight ahead in the Manhattan courtroom.

"The defendant did all of this ... because he was committed to al-Qaida's overriding goal: killing Americans," he said.

The repeated mention of al-Qaida during the government's opening statement prompted defense lawyer Peter Quijano to demand a mistrial, saying prosecutors had promised they would not claim that Ghailani was a member or associate of al-Qaida.

Prosecutor Michael Farbiarz said the government had said it had no proof Ghailani had formally pledged an oath to al-Qaida. U.S. District Judge Lewis A. Kaplan denied the mistrial request.

Lewin told jurors they would hear testimony from a former al-Qaida "insider" who has pleaded guilty. Some of the bombings' survivors also will take the witness stand, he said.

He said other evidence would include a bomb detonator found in a locked cabinet in Ghailani's apartment, a twisted and charred piece of the bomb truck Ghailani helped purchase and proof that Ghailani's clothing was covered in explosives residue.

Prosecutors also said they would show that Ghailani left Africa a day before the explosions on the same flight to Pakistan as two al-Qaida operatives.

After Ghailani fled to Pakistan, he "never dreamed that one day he would face all these witnesses ... here in an American courtroom," Lewin said during a 40-minute opening.

Defense attorney Steve Zissou, however, described Ghailani as an unwitting "dupe" for al-Qaida. His client, he said, "ran errands" for longtime friends he believed were legitimate businessmen — not terrorists.

Unlike others involved in the plot, Ghailani "did not go to training camps. He did not get indoctrinated," the lawyer said. "It is not his hatred. He is neither a member of al-Qaida nor does he share their goals."

Later, he added: "He was with them, but he was not one of them."

Prosecutors have accused Ghailani of being a bomb-maker, document forger and aide to bin Laden. He has denied knowing that the materials he delivered would be used to make a bomb.

Ghailani, 36, faces a life sentence in prison if he is convicted of conspiring with others, including Osama bin Laden, to blow up embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania, in August 1998.

In Tanzania, there was "a low rumbling noise" followed by a blast that blew out windows and knocked computers off desks inside the embassy, said former diplomat John E. Lange, the first witness.

He described pulling rubble off a colleague who was trapped in her office. Outside, he came across a badly burned man.

The man "was in the last gasps of life," he said.

Ghailani was arrested in Pakistan in 2004 before being held in Guantanamo.

Prosecutors were going forward without their top witness after Kaplan ruled last week that the government couldn't use him. The judge found that the man's testimony that he sold explosives to Ghailani must be excluded from the trial because the government only learned about him after Ghailani was interrogated at a secret overseas CIA camp where harsh interrogations occurred.

The Ghailani trial is the second trial in Manhattan to stem from the embassy bombings. Four men convicted at a 2001 trial are serving life sentences.

(This version CORRECTS spelling of first witness's last name to John Lange, not Lang.)