Zazi's arrival in New York last week triggered a series of raids by the FBI and New York City police intended to disrupt what authorities described as "a real deal" attempt to attack targets in New York.
Zazi, who initially denied any ties to al Qaeda, later admitted connections to the terror group and told FBI interrogators he had received explosives training at a terror camp in Pakistan.
A computer belonging to Zazi showed he had researched baseball and football stadiums and sites used in the recent Fashion Week event in New York City, law enforcement officials tell ABCNews.com.
While officials say they do not know the targets of the alleged plot, the contents of Zazi's computer are considered a valuable insight into what he might have been planning.
The officials said text messages sent by Zazi suggest the plot was nearing the attack phase. One message said the "wedding cake is ready," which authorities say may have been code to indicate the attack was ready. Al Qaeda operatives have frequently used references to weddings to disguise planned terror attacks.
Zazi's lawyer, Arthur Folsom, said his client was cooperating fully with the FBI during his long interrogation sessions. Folsom told ABCNews.com "no deal has been offered," but authorities say Zazi is preparing a "proffer" of information he would be prepared to testify about as part of a plea negotiation.
Zazi's computer was copied, or "mirrored," by FBI agents last weekend without Zazi's knowledge. His lawyer said the agents probably made the copy after towing away Zazi's car on an purported parking violation. The computer was in the car, and Zazi told his lawyer he discovered it had been tampered with when he retrieved the car at a police lot.
Authorities who have been briefed on elements of the alleged plot said it was a "varsity level" plan similar in scope to the 2005 attacks on London's subways and busses.
A recipe for homemade explosives found on Zazi's computer would have produced a bomb of the same size and type used in London, authorities said.
The suicide bombers in London used backpacks and plastic containers to carry the explosive mixtures.
Raids in New York led to the discovery of 14 new backpacks.
FBI agents in New York, Denver and other U.S. locations are "working around the clock" on the investigation, according to Attorney General Eric Holder.
The New York Daily News reported Saturday that seven New York men with ties to Zazi had unsuccessfully attempted to rent a large rental truck on Sept. 10, the day before Zazi arrived from Denver.
This story has been updated.