ABC News has identified the hotel where accused al Qaeda bomb maker Najibullah Zazi apparently experimented with store-bought chemicals and a bomb-making recipe as the Homestead Studio Suites Hotel in Aurora, Colo.
Zazi, 24, of Denver, first checked into the hotel Aug 28 after purchasing a dozen 32-ounce bottles of "Ms. Kay's Liquid" -- a hydrogen peroxide-based product, from a local beauty supply store, according to court documents filed by the Justice Department today.
Investigators say Zazi returned to the same hotel suite on Sept. 6 and 7, where he was seen on hotel surveillance cameras.
"Subsequent FBI testing for explosives and chemical residue in the suite revealed the presence of acetone residue in the vent about the stove," according to federal prosecutors.
Front desk staff at the hotel refused to comment and referred ABC News to the company's corporate headquarters, where spokeswoman Jennifer Kearney also refused to comment.
Zazi planned to use chemicals and hair care products he bought at beauty parlor supply stores to build a series of devastating bombs, according to a federal indictment made public today.
According to court documents, Zazi "purchased unusually large quantities of hydrogen peroxide and acetone from beauty supply stores in the Denver metropolitan area."
Former FBI agent Brad Garrett, now an ABC News consultant, said the alleged plot is "probably one of the more significant cases that the bureau has investigated since 9/11."
"You're talking about subway stations, public places where potentially thousands of people could be killed," said Garrett. "And in addition to that, when you add multiple locations, you're talking about potentially a horrendous number of people dying."
The chemicals in the products matched those listed in nine pages of hand written bomb-making instructions Zazi received when he attended an al Qaeda training camp in Pakistan late last year, according to officials.
The court documents filed today say other individuals traveled with Zazi to Pakistan.
"We believe any imminent threat arising from this case has been disrupted," said attorney general Eric Holder in a prepared statement. "We are investigating a wide range of leads," he added.
Liquid Developer Clairoxide, Ms. Kay's Liquid 40 Volume and Ion Sensitive Scalp Developer were among the products the government said Zazi and other un-named co-conspirators purchased this summer.
An employee at one beauty product supply store told ABCNews.com that FBI agents had shown a photo spread of three men with beards and two young, blond-haired women. One of the men was recognized as Zazi, said the employee who asked that her name not be used.
Court documents say Zazi sent text messages to the others, "each communication more urgent in tone than the last -- seeking to correct mixtures of ingredients to make explosives."
Officials told ABCNews.com that one of Zazi's text messages included the phrase, "the wedding cake is ready," which authorities believe was a code indicating the plot was nearing the attack phase.
The new indictment of Zazi was returned late Wednesday by a federal grand jury in Brooklyn, N.Y., where Zazi will be put on trial.
His lawyer had no comment on the new charge "at this time." Zazi had been arrested initially on a charge of lying to FBI agents in Denver.
The language in the court documents suggests many others were involved with Zazi in what is shaping up as the most serious attempt by al Qaeda to strike at the United States since the Sept. 11 attacks.
Authorities say when Zazi traveled to New York on Sept. 10, he stayed in an apartment in Queens where agents later found a small scale that "contained Zazi's fingerprints" and would "be suitable for performing several of the procedures outlined" in the al Qaeda bomb making instructions.
Zazi appeared in court in Denver today, and is scheduled to make another appearance Friday.
ABC News' Angela Hill, Rehab El-Buri and Joseph Rhee contributed to this report.