DENVER -- A 24-year-old Arapahoe County airport shuttle driver and his 53-year-old father made their first appearance in a Denver federal courtroom Monday to hear charges they lied to federal investigators in an ongoing terrorism probe.

The men appeared at about 1:30 p.m. handcuffed and dressed in the same clothes they were arrested in late Saturday night.

Federal Magistrate Judge Craig Shaffer read both defendants their rights and set a preliminary and detention hearing for Najibullah Zazi for Thursday at 9 a.m. He will remain in custody at least until then.

The government is not seeking to have Mohammed Zazi kept in custody, but he will be subject to certain conditions including having to restrict his travel only within the state and wear an electronic bracelet to monitor his movements. As part of his condition for electronic monitoring, he had to post a $50,000 unsecured bond, report regularly to a supervisor's office, surrender his passport, remain actively employed and cannot possess firearms or weapons. When he is under home confinement, he can only leave home to go to work, attend religious services, medical purposes, and for court appearances.

The elder Zazi will have to remain in custody for two days until the monitoring system can be set up.

Both men were being kept in a Denver jail but were moved to a federal prison in Englewood after their court appearance.

The judge also asked prosecutors if they will be presenting any sensitive evidence gathered under the Foreign Intelligence Surveillance Act at Najibullah Zazi's hearing on Thursday, which would prevent the hearing from taking place in open court.

Prosecutors said they didn't think they would.

The court appointed a federal public defender for Mohammed Zazi named Warren Williamson. He asked for a Pashtun interpreter for Mr. Zazi, a naturalized U.S. citizen who was born in Afghanistan and does not speak fluent English.

Attorney Arthur Folsom will continue to represent Najibullah Zazi.

The 25-minute hearing took place in a courtroom in the Alfred J. Arraj courthouse in downtown Denver. Both men were handcuffed and taken out of the courtroom when the hearing was finished.

Case Against Najibullah Zazi

Investigators said Najibullah Zazi played a direct role in the alleged terror plot. Investigators said they found notes on bomb-making instructions that appear to match Zazi's handwriting, and discovered his fingerprints on materials -- batteries and a scale -- that could be used to make explosives.

Publicly, law enforcement officials have repeatedly said they are unaware of a specific time or target for any possible attacks.

Privately, officials speaking on condition of anonymity because they weren't authorized to discuss the case, said investigators have worried most about the possible use of backpack bombs on New York City mass transit trains, similar to attacks carried out in London and Madrid.

About a dozen new black backpacks and cell phones were taken from apartments in the Queens raids last week, ABC News reported.

Zazi, his father, and a third man were arrested over the weekend, accused of making false statements to the government.

Ahmad Wais Afzali, 37, was arrested in New York, where he is an imam at a mosque in Queens. Afzali was to appear Monday in federal court in New York.

“You can expect more charges and more serious charges,” said former federal prosecutor Bill Taylor, who now works for Cyopsis, an IT forensics investigation company.

If convicted, they face up to eight years in prison and up to $250,000 in fines.

Legal analyst Craig Silverman said he believes the case against the older Zazi may be dismissed.

How can you say he lied when it looks like he doesn't understand English, Silverman asked.

Silverman also believes Folsom may be in over his head. He wondered what kind of attorney would let his client speak for 24 hours with FBI.

Taylor said that may not be the case.

“The question is under what terms and conditions did he agree to those interviews,” said Taylor. “It looks like he had some sort of immunity agreement in place, but that doesn’t help you if the government can prove what you said during the interview that was covered by the immunity agreement turns out to be false.”

More Arrests Ahead?

7NEWS has learned that the three men are not the only ones expected to be arrested in the case. More arrests are ahead.

Investigators said that there could be at least four more people in Colorado, and four in New York, connected to the terror cell believed to be plotting an attack. Sources told ABC News that Najibullah Zazi appears to be one of two key players. The identity of the other person is not known.

Two high-ranking law enforcement officers said there is no current operation involving the joint terrorism task force in the Denver metro area and nothing expected in the near future. The current focus is in New York, sources said.

The government alerted law enforcement nationwide about the danger of an attack on mass transit. Senior management at Regional Transportation District confirmed that it has received no special alert for a potential attack in Denver.

RTD says it continues with its post Sept. 11, 2001 levels of security but no additional security has been requested or added in the last week.

The younger Zazi has publicly denied being involved in a terror plot. Folsom dismissed as "rumor" any notion that his client played a crucial role.

Federal officials in Denver declined to comment.

Feds Say Men Lied About Conversations

Mohammed Zazi and Afzali are accused of lying to FBI agents about calls between Denver and New York. An affidavit accuses Afzali of lying about a call in which he told Najibullah Zazi that he had spoken with authorities.

Zazi's father is accused of lying when he told authorities he didn't know anyone by the name of Afzali. The FBI said it recorded a conversation between Mohammed Zazi and Afzali.

Prosecutors have said they're not seeking to detain Zazi's father. It was unclear whether they would seek to detain Afzali, who has worked as an informant for New York police.

Carl Tobias, a University of Richmond law professor who tracks such investigations, said authorities could have made the arrests because they feared too much information was getting to the suspects. Additional charges could be filed later, he said.

Ron Kuby, Afzali's attorney, has said the government may have been forced to act after Najibullah Zazi went to New York. Zazi has said he drove there in September to resolve issues with a coffee cart he owns in Manhattan.

Kuby said Monday that his client had fully cooperated with the FBI, and was aware all along that his phone calls were being monitored.

"Why in the world is he going to lie about the content of a conversation that he knew was being taped?" Kuby said outside the Brooklyn courthouse where Afzali was to appear later in the day.

He accused authorities of trying to make Afzali a scapegoat for a botched investigation.

"The government wants somebody to blame for the fact that they haven't caught any terrorists," he said.

Arrest Warrant Alleges Zazi Admits Getting Trained By Al-Quida

ABC News reported that the FBI has been following Zazi for the past year.

An arrest warrant affidavit alleges Zazi admitted to FBI agents that he received instruction from al-Qaida operatives on subjects such as weapons and explosives. It also says he received the training in the federally administered tribal areas of Pakistan.

Court documents filed in Denver say Zazi spoke with agents under an agreement where he might avoid prosecution. Zazi's defense denied reports that he considered a plea deal related to terror charges.

The FBI said it found nine handwritten pages of bomb making instructions on a laptop containing formulas and instructions for making a bomb, detonators and a fuse. Zazi told the FBI that he must have unintentionally downloaded the notes as part of a religious book and that he deleted the book "after realizing that its contents discussed jihad."

An affidavit says the handwriting on the notes appeared to be Zazi's. It also says they were e-mailed in December as an attachment between accounts believed to be owned by Zazi, including an account that originated in Pakistan.

FBI agents say Najibullah Zazi traveled to Pakistan twice this year. Zazi says he was visiting his wife, who lives in the Peshawar region.

Zazi was born in Afghanistan, moved to Pakistan at age 7 and emigrated to the United States in 1999. He returned to Pakistan in 2007 and 2008 to visit his wife, according to Folsom.

If you have any information about this case, or want to provide tips on this case, call our Call7 Investigators at 303-832-7777 or e-mail our investigative team.