The Iranian government has blamed the United States for the assassination of a Tehran University nuclear physicist, Massoud Ali-Mohammadi, on Tuesday. Iran has also accused the United States of kidnapping a nuclear scientist who disappeared during a summer pilgrimage to Saudi Arabia. Other evidence suggests that Ali-Mohammadi might have been targeted by a domestic group, due to his support for the student movement or his opposition to the Islamic Republic. Let's say Western powers really are trying to eliminate Iran's nuclear scientists: Would killing or kidnapping just one or two affect the country's weapons program?
Possibly. There's little verifiable (or at least publicly available) intelligence on the inner workings of Iran's uranium-enrichment program. Informed observers of the Islamic Republic, however, guess that many thousands of people are likely to be working on the development of nuclear weapons in some capacity. Of those, just 50 or so might be playing a critical leadership role. A well-placed explosion, then, could lead to delays, though not debilitation of the whole project. Perhaps the best target would be Mohsen Fakhrizadeh-Mahabadi, an officer in the Revolutionary Guard and professor of physics at Imam Hussein University who some Western intelligence agencies suspect is in charge of the nuclear program.
The "thousands" supposedly involved in Iran's efforts would include many minor or nonessential players: technicians, science or engineering professors at Iranian universities called in for advice or for freelance assignments, and maybe a few foreign consultants. (In October, Israel's prime minister gave the Kremlin a list of Russian scientists who may be helping Iran develop a nuclear warhead.) The 50 or so who really matter are more likely to be engineers than physicists like Massoud Ali-Mohammadi, since the difficulties Iran faces in achieving nuclear capability are probably design-related (as opposed to deficiencies in theoretical understanding). The engineers might be working on pressing matters like how to make a bomb compact enough to sit on a ballistic missile.
Although there's no evidence that the United States or Israel had any involvement in Ali-Mohammadi's death, Israel, at least, may have ordered assassinations to halt weapons programs in the past. Leading up to Israel's 1981 airstrike on Iraq's Osirak reactor, three Iraqi scientists died under mysterious circumstances. It's widely believed that Israel's intelligence agency was involved in these deaths. The private intelligence company Stratfor has advanced the theory that in January 2007, Mossad agents killed Dr. Ardeshire Hassanpour, a physicist who worked at a plant that produces uranium hexafluoride gas in Isfahan, Iran. As for why the Mossad targeted scientists instead of engineers, there are two possible explanations. Physicists are easier to identify as nuclear experts, since they leave a paper trail of publications in academic journals. They may also be more likely to play a supervising role in a weapons program.
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Explainer thanksDavid Albright of the Institute for Science and International Security, Ivan Oelrich of the Strategic Security Project at the Federation of American Scientists, Muhammad Sahimi of the University of Southern California, and Steven Simon of the Council on Foreign Relations.