In the first civilian trial of a former Guantánamo detainee, the word Guantánamo was not uttered in front of the jury as the case began on Tuesday in Federal District Court in Manhattan.

Instead, a prosecutor focused on what he said was the defendant’s role in a 1998 plot to bomb two United States Embassies in East Africa.

The defendant, Ahmed Khalfan Ghailani, participated “because he and his accomplices were committed to Al Qaeda’s overriding goal, killing Americans,” the prosecutor, Nicholas Lewin, told the jury in his opening statement. Mr. Ghailani helped to buy the truck that was used to bomb one embassy, in Dar es Salaam, Tanzania, and also about 20 large gas tanks that were packed inside the truck to increase the force of the blast and kill more people, Mr. Lewin said.

That bombing killed 11 people; a nearly simultaneous attack on the American Embassy in Nairobi, Kenya, killed 213 people. Thousands of people were wounded in the attacks, which were orchestrated by Al Qaeda’s East Africa cell.