Federal agents said the DEA and the FBI recorded a number of meetings and phone calls between the informant and Arbabsiar, some of them from Iran.
Officials said Arbabsiar flew from Iran through Frankfurt, Germany, to Mexico City Sept. 29 for a final planning session, but was refused entry to Mexico and later put on a plane to New York, where he was arrested.
Arbabsiar also reportedly told the undercover DEA informant that his contacts in the Iranian government could provide "tons of opium" for the Mexican cartels, according to officials who have reviewed the case file.
Officials said Arbabsiar is now cooperating with prosecutors and federal agents in New York, where the case has been transferred.
"Though it reads like the pages of a Hollywood script, the impact would've been very real and many lives would've been lost," Mueller said of the foiled plot.
The public defender representing Arbabsiar did not immediately return requests for comment on this report.
ABC News' Lee Ferran and Jake Tapper contributed to this report.