Three former high school classmates discussed bombing New York City cinemas, Grand Central station, Times Square and the New York Stock Exchange before targeting the city's subways, a prosecutor said at the trial for one of the men.
Once back home after receiving terror training at an al Qaida outpost, Adis Medunjanin and the others formed a sleeper cell of would-be suicide bombers that in 2009 nearly pulled off one of the most chilling terror plots since the September 11 attacks, said assistant US attorney James Loonam.
The terror network valued them for their US passports, which allowed them to slip back into the United States and "blend in" until it was time to strike, he said.
The men "were prepared to kill themselves and everyone else around them - men, women and children", Mr Loonam said during opening statements in federal court in Brooklyn. "These men came so close - within days of carrying out this attack."
Defence lawyer Robert Gottlieb countered by accusing the US government of using "inflammatory rhetoric" about al Qaida and terrorism to prevent jurors "from seeing the truth about this case". The lawyer conceded his client - a Muslim born in Bosnia - had sought to support the Taliban's struggle against US forces in Afghanistan, but denied he agreed to kill American civilians for al Qaida.
Medunjanin, 27, has pleaded not guilty to conspiracy to use weapons of mass destruction, providing material support to a terrorist organisation and other charges. The college graduate and naturalised US citizen wore a dark suit in court and had a long, dark beard.
The defendant's childhood friends from Queens, Najibullah Zazi and Zarein Ahmedzay, have previously admitted in guilty pleas that they wanted to avenge US aggression in the Arab world by becoming martyrs.
In his first public account, Ahmedzay testified for the government that Medunjanin encouraged him to follow a more radical form of Islam by giving him recordings of sermons by US-born extremist cleric Anwar al-Awlaki. "I became very radical in my views," he said. While sitting in a car outside a Queens mosque, the three men "made a covenant to go to Afghanistan and fight with the mujahedeen against American forces".
Ahmedzay testified the three men travelled in 2008 to Pakistan, where they met al Qaida recruiters who told them they would be better suited for a suicide mission in the United States. They were driven 10 hours away to a training facility protected by 20ft mud walls. After morning prayers, English-speaking terrorists taught them how to use grenades, AK-47s and other weapons, he said.
Zazi also is expected to testify about how, after moving to the Denver area, he cooked up explosives and set out by car for New York City in September 2009 to carry out the attack. He was arrested after abandoning the plan and fleeing back to Colorado.