As details of the case leak out, Zarate said we now know "why authorities were so concerned and why they decided to disrupt the case when they did" to prevent Zazi's planned attack in New York City.
"One of the main challenges for the FBI at this point is figuring out the constellation of actors," in cooperation with Zazi, Zarate said.
CBS News Justice Correspondent Bob Orr asked Zarate about a claim he heard from sources that the Zazi case is potentially the most significant terrorist investigation since 9/11.
"It's what people are saying," he replied. "What you have here that makes it so dangerous is the fact that Zazi appears to have been trained by al Qaeda in Pakistan. Appears to not only have contacts with al Qaeda but seemed to have been deployed here at the direction of al Qaeda senior leadership."
He noted that officials became increasingly alarmed when Zazi traveled cross country from Colorado to New York.
Watch the full interview above.
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