Officials questioned Mr Zazi for three days prior to his arrest
Two Afghan-born men charged with lying to officials about a plot to launch attacks in America have been denied bail at court hearings in the US.
Najibullah Zazi, 24, and Ahmad Wais Afzali, 37, were arrested last week during a police operation to shut down a suspected terror plot.
Mr Zazi's father, Mohammed, 53, was also arrested, but has been bailed, on condition that he stays at home.
Najibullah Zazi has denied having any involvement with the alleged plot.
Mr Zazi, an airport shuttle driver, and his father were arrested in their home city of Denver, while Mr Afzali was arrested in Queens, New York, where he is an imam at a mosque.
Mr Zazi, who was already under surveillance by US security officials, had recently returned from a trip to New York.
He was questioned for three days prior to his arrest on Saturday.
A legal resident of the US since 1999, Mr Zazi is alleged by government officials to have received explosives and weapons training at an al-Qaeda camp in Pakistan last year.
Investigators have also told the media that bomb-making instructions were found in Mr Zazi's house.
In a telephone interview with the Denver Post newspaper on Saturday, Najibullah Zazi denied media reports that he had admitted any link to al-Qaeda or involvement in terrorism.
"It's not true," Mr Zazi said. "I have nothing to hide. It's all media publications reporting whatever they want. They have been reporting all this nonsense."