After overnight arrests this weekend in the alleged New York terror plot, FBI agents believe an active terror cell directed by al Qaeda was preparing an attack on New York City, and authorities say they have yet to identify everyone involved.
Officials tell ABC News they know of three distinct teams of four men each, but there may be others linked to the plot that remain unidentified.
Law enforcement agents say they're watching a number of people on round-the-clock surveillance who they suspect might have been part of the alleged terror cell.
Suspects Najibullah Zazi, a 24-year-old airport shuttle driver, and his father Mohammed made their first court appearance in a Denver federal courtroom today, handcuffed and dressed in the same clothes they were arrested in Saturday night.
Click here to watch Zazi denying al Qaeda ties to television cameras.
They are charged with lying to federal agents during an investigation into the alleged terror plot that has been described as "the real deal" by authorities.
Zazi is set to have a preliminary and detention hearing Thursday morning and will remain in custody at least until then. The government is not seeking to keep his father, who was appointed a federal public defender, in custody, but his travel will be restricted to Colorado and he'll wear an electronic monitoring bracelet. He will have to remain in custody for two days until the monitoring system is set up.
Zazi, who authorities say appears to be the ringleader of the alleged plot, has been tracked by the FBI and the CIA for more than a year, during which time he has traveled twice to Pakistan for explosives training from al Qaeda.
Officials say they do not have specifics on the potential targets of the alleged plot, which may have been the most serious plan against the U.S. since 9/11.
Court records show Zazi ran up more than $50,000 in debt on 20 credit cards, leading to concerns he was preparing for a suicide mission. He declared Chapter 7 bankruptcy in Mar. 2009, and while he told investigators he had been traveling toPakistan see his wife, he checked the "not married" box on his application form.
In a criminal complaint, the FBI alleges they found nine handwritten pages on the manufacture and handling of explosives, detonators and the fuzing system in Zazi's possession.
"When [Zazi] was questioned about whether or not he knew anything about these written notes, and they were shown to him, he denied that knowledge," said NYPD Commissioner Ray Kelly.
Kelly said Mohammed Zazi was arrested "because he lied about the phone call that he made to his son when he was in New York."
Imam Ahmed Afzali
The third man arrested this weekend, Queens, NY resident Ahmed Afzali, appeared in a Brooklyn court today but no plea was entered. He is scheduled to have a detention hearing Thursday morning.
Afzali is also charged with making false statements to federal agents. He is alleged to have falsely told authorities that he didn't tell the Zazis he had been asked by officials about them.
Afzali's attorney Ron Kuby told ABC News that his client, a respected imam at a Queens, NY mosque who had worked as a source for law enforcement in the past, was doing what authorities asked him to do.
"It was the government that went to him and said we need to know the whereabouts of Najibullah Zazi," Kuby said. He said that Afzali then reached out to others to find Zazi, located and spoke to him, and then "duly reported this to the FBI."
"Now the FBI claims he didn't report everything, or he stated some details of the conversation wrong, so they arrest him," Kuby said. " So this is his reward for being a good member of the community."
Kuby said his client would plead not guilty.
Aaron Katersky contributed to this report.