The government credits Hussain with rooting out radical Muslims at a mosque in Newburgh, a small town north of New York. The defense has sought to portray him as a "fraudster" who lured down-and-out dupes into a phony scheme by offering them a pile of cash.
Hussain's credibility will be tested as the government's star witness at the trial, which is set to begin with opening statements this week in federal court in Manhattan.
James Cromitie, Onta Williams, David Williams and Laguerre Payen have pleaded not guilty to charges that they engaged in a conspiracy to use weapons of mass destruction and conspiracy to acquire and use anti-aircraft missiles to kill U.S. officers and employees. They face possible life prison terms if convicted.
Authorities last year called the case a "chilling plot" involving "extremely violent men" who represented a growing, dire homegrown terrorism threat. But the government also concedes the men - targets of an elaborate, tightly scripted sting involving fake weapons, 100 officers and a spy plane - had no ties to actual terrorists.
Pressing that point with prosecutors, U.S. District Judge Colleen McMahon said at a recent hearing she had been referring to the case privately as "the un-terrorist case" The trial is "going to be about whether these guys were going to blow something up," Assistant U.S. Attorney David Raskin said at the hearing. "It's not going to be about al-Qaida, and it's not going to be about foreign terrorist organizations."
The case began in June 2008, when Hussain struck a conversation with Cromitie, whom he met by chance in the parking lot of the Newburgh mosque.
Hussain was posing as a wealthy representative of a Pakistani terrorist organization. He drove a BMW and other luxury vehicles provided by the FBI to maintain his cover. Cromitie was a convicted drug dealer working odd jobs.
Prosecutors allege that within minutes of meeting Hussain, Cromitie told him, "I want to do something to America."
During subsequent meetings over the next several months, Cromitie "presented himself to (Hussain) as a rabid anti-American, Jew-hating radical Muslim with a healthy penchant for violence and a deeply held desire to avenge the injustices that in his eyes had befallen Islam and Islamic people around the world," prosecutors said in court papers.
The government says Cromitie - with Hussain playing "terrorist facilitator" - eventually hatched a plot involving the other men to blow up two synagogues in the Bronx with remote-control bombs.
They also wanted to use surface-to-air missiles to shoot down planes at the Air National Guard base in Newburgh.
The explosives and missile system that the men thought they had obtained actually were inert devices supplied by the FBI. An airplane, a helicopter and a camera planted inside a car were videotaping the men on May 20, 2009, when they went to the synagogues to plant the fake bombs.
The explosives "were positioned to blow up hours later by remote control, as soon as they shot missiles at military planes," prosecutors wrote in court papers.
"By the time it was over, the FBI had arrested four men dangerous enough to willingly, even enthusiastically, join forces with a man who presented himself as a terrorist desiring to blow things up for the 'cause' of Islam."
The defense claims the sting amounted to entrapment. Lawyers argued in court papers that nothing would have happened with Hussain, who "proposed, directed, supplied, funded and facilitated every aspect of the 'terrorist' plot with which the defendants are charged."
They cite recordings from April 2008 they say show Cromitie had serious doubts about going forward with the plan, prompting Hussain to suggest he would be passing up a big pay day.
"I told you, I can make $250,000, but you don't want it brother," Hussain said. "What can I tell you?"
Two days later, lawyers say, the alleged mastermind still was wavering.
"I don't know what to do with my life right now," Cromitie said. "I don't know. I'm struggling. I don't have to do anything crazy."