NEW YORK -- Investigators have identified possible accomplices of a Colorado man accused of plotting a terrorist attack on New York, a law enforcement official said Monday, but the whereabouts of the helpers or any bomb-making materials they procured are unclear.

Court papers allege that at least three people helped Najibullah Zazi buy beauty products containing peroxide and acetone in Aurora. The chemicals can be used to make homemade bombs.

Investigators know the identities of the three people, who are from New York City, the law enforcement official told The Associated Press on Monday. He spoke on condition of anonymity because the investigation continues.

The official would not say anything about where the possible accomplices or the bomb-making materials are.

Zazi, an Afghan immigrant who moved to Colorado in January of this year, had pages of notes detailing how to turn the beauty products into explosives and at least 18 bottles of peroxide-based hair lighteners, authorities have said.

A surveillance camera shows Zazi purchasing the hair products at the Beauty Supply Warehouse on 6th Avenue in Aurora. An indictment accuses Zazi of going to a nearby hotel afterward to mix up the chemicals.

Zazi has proclaimed his innocence. His lawyer said authorities have no explosives or chemicals to back up claims that he planned an attack in New York City to coincide with the anniversary of the Sept. 11, 2001 attacks.

As authorities have continued to search for additional suspects, they've issued a flurry of terrorism warnings for sports complexes, hotels and transit systems based on their investigation.

Prosecutors have said the three others who shopped with him in Aurora for the beauty products also accompanied him on an August 2008 flight to Pakistan for terrorism training. By that time, he had already come to authorities' attention.

Law enforcement sources said the three men bought the beauty products with stolen credit cards.

A criminal complaint has suggested that police, acting without the FBI's knowledge, might have compromised the investigation and helped blow the surveillance of Zazi by questioning a Muslim religious leader about him.

The imam and Zazi's father face charges of lying to terrorism investigators; they deny the allegations.

Zazi's father, Mohammed Zazi, was scheduled to return to federal court for an administrative hearing but that hearing was canceled and rescheduled for a later date.

Najibullah Zazi is expected to appear in a New York courtroom at 9 a.m. MST. At that time, he will be arraigned on the charge of conspiracy to use weapons of mass destruction. His attorney, Art Folsom, has already told 7NEWS they will enter a plea of not guilty.