An immigrant from Afghanistan who lived legally in Denver was plotting one of the most serious terrorist attacks on American soil since Sept. 11, 2001, federal authorities say.
Najibullah Zazi, 24, made his home in the United States, working as a Denver airport shuttle driver in Colorado and owning a coffee cart in New York City.
Authorities say Zazi scoured the Web and visited beauty supply stores in a hunt for chemicals needed to build bombs for Al Qaeda.
They characterized the suspected plot against New York City subways and trains as one of the most significant threats to the United States since 9/11.
In the 12-page memorandum outlining the alleged conspiracy, authorities repeatedly referred to "others," evidence of a possible Al Qaeda cell plotting a homemade bomb attack on U.S. soil.
Zazi was charged in New York City with conspiracy to use weapons of mass destruction.
He was ordered held without bail Friday in a Denver federal courtroom and was transferred to New York to face the terrorism conspiracy charges.
Lesser charges of lying to the federal government were dropped Friday.
Since Zazi's weekend arrest, investigators have fanned out over New York City, going to beauty shops, home improvement stores and neighborhoods Zazi frequented looking for possible accomplices, while the government issued national terrorism warnings for sports complexes, hotels and transit systems.
Prosecutors said they have yet to establish exactly when and where the Zazi attacks were supposed to take place. But Attorney General Eric Holder said in Washington, "We believe any imminent threat arising from this case has been disrupted."
A law enforcement official told The Associated Press on Thursday that Zazi had associates in New York who were in on the plot. 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 beauty supply stores in the Denver area, products with names like Ion Sensitive Scalp Developer and Clairoxide.
He searched a Queens home improvement store Web site for another ingredient needed to make a compound called TATP (Triacetone Triperoxide), the explosives used in the London bombings that killed over 50 people, prosecutors said.
Zazi has publicly denied being a terrorist since his arrest. He left a Denver court Thursday without commenting.
The government motion seeking to deny bail laid out a chronology of the alleged scheme, which prosecutors said had been in the works for over a year.
Zazi — a legal U.S. resident who immigrated in 1999 — began plotting as early as August 2008 to "use one or more weapons of mass destruction," when he "and others" traveled from Newark, N.J., to receive explosives training in Pakistan, prosecutors said.
Within days of returning from Pakistan in early 2009, he moved to the Denver suburb of Aurora, where he used a computer to research homemade bomb ingredients and to look up beauty supply stores where he could buy them, according to prosecutors.
A second law enforcement official who spoke on condition of anonymity because of the ongoing investigation said associates of Zazi visited Colorado from New York to help him buy the chemicals, using stolen credit cards to make the purchases before returning to New York.
Security video and receipts show that some of the purchases were made near a Colorado hotel, according to court papers. On Sept. 6 and 7, Zazi checked into a suite at the hotel with a kitchen and a stove, the 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. "Each communication" was "more urgent than the last."
FBI explosives testing later found residue in the vent above the stove, authorities said.
On Sept. 8, court papers say, Zazi searched the Internet for home improvement stores in Queens before driving a rental car for a two-day trip to the city. The visit triggered a series of searches in Denver and New York City over the past two weeks, and netted backpacks, cell phones and a scale at a home where Zazi spent the night.
A law enforcement official said Thursday 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, and considered arresting him right away. The official spoke on condition of anonymity because the investigation continues.
Beauty supply store employees in New York and the Denver suburbs said authorities had been there recently 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.
Zazi's father, Mohammed Wali Zazi, and a New York City imam, Ahmad Wais Afzali, also appeared in court Thursday on charges they lied to investigators. Mohammed Zazi, 53, was ordered freed under court supervision in Denver until an Oct. 9 hearing. Afzali, who was accused of tipping off the Zazis to the federal probe against them in a tapped telephone call, was released in New York on $1.5 million bail.
Afzali's attorney, Ron Kuby, denied his client knew anything about a plot.
"Obviously, the government would not be consenting to bail if it thought he was involved in a terrorism conspiracy," he said.
In unrelated terrorism cases elsewhere around the country Thursday:
— Michael C. Finton, a 29-year-old man who idolized American-born Taliban soldier John Walker Lindh, was arrested after attempting to detonate what he thought was a bomb inside a van outside a federal courthouse in Springfield, Ill., officials said. FBI agents had infiltrated the alleged plot months ago.
— A 19-year-old Jordanian was arrested after placing what he thought was a bomb at a downtown Dallas skyscraper, federal prosecutors said. The decoy device was provided by an undercover FBI agent. Federal officials said the case against Hosam Maher Husein Smadi, who is charged with attempting to use a weapon of mass destruction, is unrelated to the Illinois case.
— Two North Carolina men under arrest since July on international terrorism charges were also accused by prosecutors of plotting to kill U.S. military personnel.
The Associated Press contributed to this report.