A former prosecutor says authorities' refusal to discuss the whereabouts of three people alleged to have helped a suspected Al Qaeda operative buy beauty supplies to make explosives might mean the accomplices have left the country or are secretly cooperating.

The suspect, Afghan immigrant Najibullah Zazi, pleaded not guilty Tuesday to plotting a bomb attack in New York. Police Commissioner Raymond Kelly pronounced the threat neutralized and said there is nothing to fear from Zazi's three alleged accomplices.

PHOTOS: Alleged NYC-Denver Terror Plot

The terror scheme "has been broken up," Kelly said. "I see no danger emanating ... from the people involved in this investigation."

He would not elaborate. But former federal prosecutor Harry Sandick said that might mean the three are not in the U.S. or may have agreed to cooperate with the investigation.

"One would think they're in custody or likely to be in custody soon," Sandick said.

Police also said there are no extra security measures in place in subways or elsewhere in New York because of the alleged plot.

Zazi, 24, is the only suspect publicly identified so far in what Assistant U.S. Attorney Jeffrey Knox called a conspiracy that was "international in scope." Prosecutors said Zazi received Al Qaeda explosives training in Pakistan last year and may have intended to carry out his attack on the anniversary of 9/11.

After his return to the U.S., authorities said, three people traveled from New York City to suburban Denver over the summer and used stolen credit cards to help Zazi buy products containing hydrogen peroxide and acetone — common ingredients for homemade bombs.

Authorities said the three returned to New York at some point.

Zazi, heavily bearded and wearing a blue jail smock, never spoke and showed no emotion as his lawyer entered a not guilty plea to conspiracy in a Brooklyn courtroom guarded by a team of deputy marshals. He was ordered held without bail.

"You get the impression he's a nice guy, don't you?" defense attorney Michael Dowling said to reporters afterward.

Dowling acknowledged that the Denver airport shuttle driver visited Pakistan last year and made purchases this year at a beauty supply shop in Aurora, Colo. But he added, "Those acts are not illegal" and cautioned against a "rush to judgment."

Asked about possible accomplices, the lawyer said: "I don't know the names of anybody else that allegedly conspired with Mr. Zazi. ... Those names have not been produced."

Investigators said Zazi urgently tried to mix explosives in a Colorado hotel room in early September, then drove to New York to carry out an attack, perhaps on the New York transit system.

The FBI was listening in and becoming increasingly concerned as the anniversary of the Sept. 11, 2001, attacks and a New York visit by President Barack Obama approached, officials said.

On Sept. 10, investigators secretly searched Zazi's rented vehicle in New York and found a laptop computer with bomb-making instructions, authorities said.

Zazi, fearing he was being watched, flew back to Denver on Sept. 12, authorities said. He was arrested a week later.

Zazi's next court date was set for Dec. 3.

More coverage from MyFOXNY.com.