But after they discovered he had made the first video, in April, "they relocated me from Tucson to Virginia with guards all around me and until this moment, I've been monitored by armed agents."
"They put more psychological pressure on me. They told me they would kill me ... . They threatened me every time," Amiri said.
Amiri had originally "left his family behind, that was his choice," said a US official who was briefed on the case, speaking on condition of anonymity because the official was not authorized to talk publicly about the case.
Vincent Cannistraro, a retired CIA officer, said he believes Amiri was not recruited by the CIA but volunteered to provide information to the agency about Iran's nuclear program over a period of years before he came to the US Cannistraro said he believed that after Amiri's defection, the Iranian government threatened to harm his son as leverage to get him back to Tehran.
"It certainly was an embarrassment to the Iranian government, and clearly they wanted him back," Cannistraro said.
Amiri, flying home via Doha, Qatar, was expected to arrive in Tehran early Thursday. It is unclear what sort of reception he will receive.
Iran's Foreign Minister Manouchehr Mottaki said: "For certain, after his return ... we will speak with him about it all in greater detail," Manouchehr Mottaki said.
"We will examine his circumstances. It's obvious it was a kidnapping," Mottaki told reporters through a translator during a visit to Lisbon, Portugal. "We reserve our right to pursue this case as we see fit."
Before he disappeared, Amiri worked at Tehran's Malek Ashtar University, an institution closely connected to the country's powerful Revolutionary Guard.
State Department spokesman P.J. Crowley said he does not know what Amiri may have told US officials, but that the US government "maintained contact with him" during his stay in the United States. Pressed whether Amiri was a defector, Crowley replied, "I just don't know the answer."