Shahawar Matin Siraj, 23, faces a maximum life sentence after a Brooklyn federal court jury convicted him on Wednesday of conspiring to place and detonate an explosive on the city's mass transit system, among other charges.
Siraj and another man suspected in the plot, James Elshafay, were arrested in 2004 carrying crude diagrams of their target -- the underground station in Herald Square, a busy shopping district that includes Macy's department store.
Elshafay immediately agreed to co-operate with the government.
The authorities say Siraj had no affiliation with known terrorist organisations. Instead, he caught the attention of an informant, Osama Eldawoody, and an undercover police officer with his anti-American rants at an Islamic bookstore where he worked.
Eldawoody, a naturalised US citizen from Egypt, and the Bangladesh-born undercover officer both testified for the government.
The informant had been assigned by the New York Police Department to identify and monitor extremists in the city's Muslim neighbourhoods following the September 11 attacks.
Eldawoody testified in 2003 and 2004 that he was paid more than $100,000 to report about daily mosque activities, including prayers.
"That [rumours that US troops were sexually abusing Iraqi girls] was enough for me. I'm ready to do anything. I don't care about my life"
Shahawar Matin Siraj,
secretly caught on tape
Siraj questioned new powers granted to police after they lobbied for increased surveillance of mosques they believed could harbour extremists.
The undercover officer, who testified using an alias, described being plucked straight out of the police academy in 2003 and given orders to become a "walking camera" among Muslims.
He said Siraj openly supported al-Qaeda leader Osama bin Laden.
Inflamed by Abu Ghraib
Inside the bookstore, Eldawoody wore a wire and chatted with Siraj. When the topic turned to the war in Iraq, the defendant recounted rumours that US soldiers were sexually abusing Iraqi girls.
"That was enough for me," Siraj said in one of a series of secretly recorded conversations played for the jury. "I'm ready to do anything. I don't care about my life."
On tape, Siraj was heard musing about possibly destroying the Verrazano-Narrows and three other bridges serving Staten Island or killing Bill Gates, the chairman of Microsoft.
Testifying in his own defence last week, Siraj said he never had a violent thought before he fell under the spell of the 50-year-old Eldawoody.
"I used to just listen to him (police informant Eldawoody), but I never said 'Yes, I was going to do it' or 'no' until the Abu Ghraib thing came up"
He said the older man became a mentor and instructed him that there was a fatwa (religious edict) permitting the killing of US soldiers and law enforcement agents.
Martin Stolar, Siraj's lawyer, argued that his client was "not the brightest bulb in the chandelier" and was easily led by Eldawoody.
Eldawoody had himself talked about "blowing up the buildings and blowing up the Wall Street places", the defendant said.
He admitted taking steps to attack the underground station, but only after the informant inflamed him by showing him photos of prisoners being abused at Abu Ghraib prison in Iraq.
"I used to just listen to him, but I never said 'Yes, I was going to do it' or 'no' until the Abu Ghraib thing came up," Siraj said.
Ray Kelly, the New York police commissioner, welcomed the verdict as "an important milestone in safeguarding New York against terrorist plotters whether home-grown or foreign".