A former senior intelligence official involved in efforts to thwart Iran's nuclear program told ABC News that assassinations of top Iranian scientists were usually assumed to be the work of Israel, but that the Israelis would never confirm or admit responsibility.
"Every time we ask," said the official, "they just smile and say, 'We have no idea what you are talking about.' "
The U.S., for its part, has officially denied any involvement in the deaths of Iranian scientists. A White House spokesman called the accusations "absurd" after Mohammadi's death. The CIA is known, however, to have recruited scientists as spies.
In 2007, after Iranian General Ali-Reza Asgari went missing in Turkey, the Iranian government said the intelligence official had been kidnapped by Mossad. The Israeli and Western media said he had defected, and was busy providing information on Iran's nuclear program.
Two years later, award-winning Iranian nuclear scientist Shahram Amiri disappeared while on a pilgrimage to Mecca. He later resurfaced in the United States after defecting to the CIA in return for a large sum of money, according to people briefed on the operation by intelligence officials. A spokesperson for the CIA declined official comment.
Amiri, a nuclear physicist in his early 30s, worked at Tehran's Malek Ashtar University, which is closely connected to Iran's Revolutionary Guard, according to the Associated Press.
When Amiri disappeared, Iran's Foreign Minister, Manouchehr Mottaki, and other Iranian officials blamed the U.S. for "kidnapping" Amiri.
After resurfacing in the U.S., Amiri released two videos, one in which he claimed he was kidnapped by the CIA, and another in which he denied he was kidnapped. He later repeated the kidnapping story publicly, said he had "escaped" from the CIA, and returned to Iran.
Amiri was recruited by the CIA because his relatively young age -- he was not 30 when he first began to work for the Americans -- and his proximity to more senior Iranian nuclear scientists would allow the CIA to collect intelligence on the program for many years, according to a U.S. official involved in the Amiri operation.
In January 2011, a dissident website reported that Amiri was being held in a Tehran prison and had been tortured.