(CNN) -- In their investigation into an alleged plot to kill Saudi Arabia's ambassador to the United States, U.S. federal agents interrogated suspect Manssor Arbabsiar for 12 days, a senior counterterrorism official said Tuesday.
Cooperation from Mexican officials played a key role in the investigation, the official said. U.S. authorities arranged with Mexican officials for Arbabsiar to be denied entry into Mexico, the official said.
From there, he was placed on an airplane to New York, where he was taken into custody and quietly taken to a secret U.S. government facility on September 29, the counterterrorism official said. U.S. agents interviewed him there every day, obtained a confession and compiled dozens of intelligence reports, the official said.
Arbabsiar, a 56-year-old naturalized U.S. citizen, and Gholam Shakuri, an Iran-based member of Iran's Revolutionary Guard, are accused of conspiracy to murder a foreign official, conspiracy to use a weapon of mass destruction and conspiracy to commit an act of terrorism, an FBI agent's affidavit released Tuesday alleged.
Shakuri remains at large, the FBI said.
U.S. Attorney General Eric Holder said elements of the Iranian government directed the alleged plan.
Investigators have directly linked the plot to Iran's Quds Force, but have not directly linked it with Iranian President Mahmoud Ahmadinejad, the senior counterterrorism official said.
Each day before he was questioned, authorities gave Arbabsiar notice that he had a right to an attorney and to be presented before a magistrate, the official said. Arbabsiar signed a waiver each day, the official said. He was presented in a New York court Tuesday after he refused to sign the waiver.
Arbabsiar was flown to New York instead of being brought into the country through Texas because agents wanted to conduct intelligence interviews, which would not have been possible under Texas law, according to the official.