Inside the '09 plot to bomb NYC subways

(CBS News) September 2009 might have been one of those dates etched in our history. That is when al Qaeda terrorists planned to walk onto New York City subway trains and into Grand Central Terminal with bombs in their backpacks. Those trains are ridden by more than 5 million people each day.

Details of the plot came from an admitted terrorist -- now a government witness -- at the trial of an alleged co-conspirator. CBS News correspondent Bob Orr is following the case.

These notes are the handwritten recipe for bombs Najibullah Zazi hoped to explode on New York subway trains. The nine pages of instructions were written by Zazi in 2008, after he attended al Qaeda training classes in Pakistan.

The notes, complete with scientific formulas and diagrams of lab beakers, detail how to build bombs with cooking oil, nail polish remover, hair bleach and ball bearings.

Watch a video below of Najibullah Zazi talking about the downloaded book which bomb-making information came from:

Zazi's homemade explosives guide was revealed in a New York courtroom Thursday where Zazi testified against an alleged accomplice.

Would-be subway suicide bomber Najibullah Zazi speaks
More on "The plot that almost happened"

Zazi, the son of Afghan parents, spent his teenage years in New York and later moved to Colorado. He's pleaded guilty to planning the failed 2009 subway attacks.

But newly released tapes of his FBI interviews show Zazi initially denied the plot. He explained the bomb-making notes came from a book he downloaded and then quickly discarded.

"As soon as I see it was and I say...this is not something I need to see or it has to be in my computer right away I delete it," said Zazi on tape.

Zazi also denied owning bomb-making equipment, like a scale needed to measure ingredients.

Watch a video of Zazi talking about a scale used to measure ingredients in relation to making bombs:

"I don't possess any one, any scale, but I think one scale...it's...my family had it to use to make maybe cakes and things," said Zazi again on tape.

But Zazi conceded a scale was found in his luggage. He was arrested four days later.

Newly released emails also show Zazi stayed in regular touch with his al Qaeda handlers, right up to the point where he became spooked by police surveillance and abandoned the plot

For example, as he was preparing explosives inside a Denver motel just before driving to New York, Zazi sent a series of messages asking for help. He wrote: "...i do not khow the amount plz right away [sic]..."

Watch Zazi talk about his childhood below:

But, Zazi also sought to assure al Qaeda the plot was on. Using a familiar Jihadi code, he wrote: "...the marriage [sic] is ready..."

In pleading guilty to the plot, Zazi promised at the time to testify against other terror suspects whenever the U.S. government calls. And he's been an active source of information, meeting with the FBI and others some 40 times in the past two years.