U.S. Magistrate Judge Craig Shaffer ultimately ordered Zazi's transfer to New York, and Zazi was taken there by federal marshals.
"No traces of any kind of chemical was found in his vehicle," Folsom said of an FBI search of Zazi's car.
A federal prosecutor argued that Zazi was planning an attack to coincide with the /*9/11*/ anniversary.
"The evidence suggests a chilling, disturbing sequence of events showing the defendant was intent on making a bomb and being in New York on 9/11, for purposes of perhaps using such items," prosecutor Tim Neff told Shaffer.
Zazi was stopped by police on Sept. 10 as he entered New York, and he dropped his plans for an attack once he realized that law enforcement was on to him, prosecutors allege.
Prosecutors said Zazi received explosives training from al-Qaida in Pakistan and returned to the U.S. bent on building a bomb.
Over the summer, he and three associates went from one beauty-supply store to another in a Denver suburb buying chemicals to make explosives like those that killed dozens of people in transit bombings in London and Madrid, investigators said.
At least three and possibly more of his accomplices remain at large, and investigators have fanned out across New York in pursuit of suspects. Authorities also issued a flurry of terrorism warnings for sports complexes, hotels and transit systems.
A law enforcement official who spoke on condition of anonymity because of the ongoing investigation said associates of Zazi visited Colorado to help him buy the chemicals using stolen credit cards before returning to New York.
Another law enforcement official said that authorities had been especially worried about Zazi's Sept. 10 visit to the city because it coincided with a visit by President Barack Obama. Police considered arresting him right away. The official spoke on condition of anonymity because the investigation continues.
Police have been especially active in the neighborhood in Queens where Zazi visited during his New York trip, staying at an apartment with a group of cab drivers and food cart operators he knows.
Folsom said prosecutors lack direct evidence that Zazi was involved in bomb-making, finding none of those materials in Zazi's car, his Aurora, Colo., apartment or apartments Zazi visited in New York. FBI agents said they found Zazi's fingerprints on a scale and batteries during a search in Queens, but Folsom said those items have no connection to the alleged plot.
"I think they were hoping that people would just jump to conclusions," Folsom said in an interview with The Associated Press.
Zazi ran a coffee cart in Manhattan before moving to Denver this year and getting a job as an airport shuttle driver.
FBI raids beginning Sept. 14 rattled a quiet, predominantly Asian neighborhood in Queens. Muslim men said dozens of FBI agents ransacked their homes and questioned them for hours, sometimes taking DNA samples and prints from their shoes.
The FBI has also been visiting beauty shops and home-improvement stores in Colorado and New York for details about the alleged bomb-making purchases.
Court papers say that during the summer, Zazi and three unidentified associates bought "unusually large quantities" of hydrogen peroxide and acetone - a flammable solvent found in nail-polish remover - from Denver-area beauty supply stores. The products had names such as Ion Sensitive Scalp Developer and Ms. K Liquid 40 Volume.
Zazi also searched the Web site of a Queens home-improvement store for another ingredient needed to make a compound called TATP (triacetone triperoxide), the explosives used by shoe bomber Richard Reid and the terrorists who carried out the London bombings that killed more than 50 people, according to court papers.
Zazi intensified his bomb-making experiments this month, cooking up substances in a Colorado hotel suite he rented on Sept. 6-7 before driving 1,600 miles to New York over the course of about two days. He became aware that law enforcement was onto him when he was stopped entering the city on Sept. 10, causing the plot to unravel.
Neff said Zazi "was in the throes of making a bomb and attempting to perfect his formulation" and seeking information on how to use flour to make the explosive suitable for transporting.
"He was asking for information on flour and how to get the contents right," Neff said in court.
The Metropolitan Transportation Authority - which runs New York City's subway system, buses and commuter rails - declined to comment on the revelation of a Sept. 11-timed plot. It reissued a statement from earlier in the week that it has boosted its police presence at "key commuter rail locations" since the terror threat became public.
Federal agents and police officers in New York visited up to 200 locations a day in the area during the probe, including beauty-supply stores, extended-stay hotels that have rooms with kitchens, hardware stores, truck rental agencies and storage facilities.
Zazi was scheduled to appear in federal court Tuesday in Brooklyn.
A government request to deny bail laid out a chronology of the alleged scheme, which prosecutors said had been in the works for more than a year.
On Sept. 6 and 7, Zazi checked into a suite at a Colorado hotel with a kitchen and a stove, government papers say, and tried to contact an unidentified associate "seeking to correct mixtures of ingredients to make explosives."
"Zazi repeatedly emphasized in the communications that he needed the answers right away," the papers said, adding that each communication was "more urgent than the last."
Beauty supply store employees in New York and the Denver suburbs said authorities had been asking whether anyone had come in buying a lot of hydrogen peroxide or acetone.
At Beauty Supply Warehouse in suburban Denver, Paul Phillips said a co-worker told investigators he had sold chemicals to Zazi. Company President Karan Hoss said the firm turned over security video of a man matching Zazi's description to the FBI. A check of sales found that someone bought a dozen 32-ounce bottles of a hydrogen peroxide product in July. More was purchased in late August, Hoss said.
Associated Press writers Tom Hays and Colleen Long in New York, Devlin Barrett in Washington, D.C., and Catherine Tsai in Colorado contributed to this report.