In January of this year, Iranian scientist Mostafa Ahmadi Roshan was commuting to work when a motorcyclist attached a magnetized bomb to the side of his car.  The resulting explosion killed both Roshan and his bodyguard-driver, and Iranian accounts report that the assassin escaped back into the early morning rush hour traffic. Roshan's is only the latest in a string of deaths and disappearances that have thinned the ranks of Iran's top physicists and exacerbated international tension over Iran's nuclear program. Similar attacks in 2010 killed nuclear specialist Majid Shahriari and and injured another nuclear physicist, Fereydoon Abbasi, who now runs Iran's Atomic Energy Organization. As early as 2007, nuclear scientist Ardeshir Hosseinpour reportedly died of gas poisoning.  Roshan also had nuclear ties; in addition to his work as a professor, he also served as a department supervisor at a uranium enrichment plant.
While most of the dead scientists were explicitly involved with Iran's nuclear program, some were not known to be nuclear specialists. For instance, some reports have raised suspicions that physics professor Massoud Mohammadi, killed by a bomb in early 2010, had links to Iran's nuclear program.  However, his professional physics work was in quantum field theory and elementary particle physics, and it is unclear what role, if any, he might have played in Iran's nuclear enrichment program.  Both he and Shahriari were associated with a project known as SESAME, or Synchrotron-Light for Experimental Applications in the Middle East, but it is considered a purely nonnuclear research unit which typically involves scientists from Israel and elsewhere in the region. 
In the wake of Roshan's assassination, Iran has reasserted its intentions to continue pursuing nuclear technology and has called for retribution against those responsible for the scientists' deaths. [5,6] Iran has openly accused the United States and its allies, particularly Israel, of sponsoring these assassinations in an attempt to sabotage its nuclear energy program. While no one has officially claimed responsibility for the attacks, Israel has issued only vague denials, and military officials have expressed little sympathy for the dead scientists.  The Obama administration, on the other hand, has both denied any involvement and issued strong condemnation of the attacks. The international community's split reaction to these events has highlighted a critical ethical question: should scientists with nuclear knowledge be treated as instruments of war?
In the United States, where suspicions are strong that Iran is working toward a nuclear weapon, opinion on this matter remains divided. For instance, Republican presidential candidate Rick Santorum recently opined that the US "should have kept [its] mouth shut" rather than condemning Roshan's death.  He and fellow candidate Mitt Romney have both come out in favor of more aggressive military action against Iran. Romney has even gone so far as to claim that re-electing Obama will ensure that "Iran will get a nuclear weapon." [7,8] As the presidential election draws nearer, politicians on both sides of the debate face mounting pressure to take a strong stance against nuclear proliferation. Obama himself, who has generally favored economic sanctions over military action against Iran, recently declared that he "will take no options off the table" to prevent Iran from achieving nuclear capabilities. 
While Romney and Santorum appear to favor air strikes against nuclear facilities, where does the distinction lie between a piece of dangerous technology and an individual with the potential to help develop it? Furthermore, how relevant to nuclear weapons must a scientists' work be before he is considered a threat? Many of the brilliant scientists recruited to work on the Manhattan Project had done their previous research on non-nuclear topics, and many went on to do vital work across the spectrum of physics research. For instance, renowned physicist Richard Feynman joined the atomic program immediately after completing an unrelated thesis on theoretical quantum mechanics, and he went on to make mostly theoretical contributions after the completion of the Manhattan Project, including his Nobel Prize winning work in quantum electrodynamics. In their effort to appear tough on nuclear proliferation, American politicians risk fostering a culture that treats all science with irrational suspicion and validating the idea that any student of nature, no matter how obscure or impractical his work, represents a valid military target.
 A. Cowell and R. Gladstone, "Iran Reports Killing of Nuclear Scientist in 'Terrorist' Blast," New York Times 11 Jan 12.
 Y.Yong and R. F. Worth, "Bombings Hit Atomic Experts in Iran Streets," New York Times, 29 Nov 10.
 "Bomb Blast Kills Iranian Professor," Al Jazeera, 12 Jan 10.
 A. Cowell, "Blast Kills Physics Professor in Tehran," New York Times, 12 Jan 10.
 R. Gladstone, "Iran Signals Revenge Over Killing of Scientist," New York Times, 12 Jan 12.
 "Tehran Explosion Kills Nuclear Scientist in Tehran," BBC News, 11 Jan 12.
 T. Beaumont, "Santorum: US Wrong to Condemn Iran Scientist Death," Chicago Sun-Times, 14 Jan 12.
 M. Landler, "Iran Face-Off Testing Obama the Candidate," New York Times, 16 Jan 12.
 L. MacInnis, "Obama: No Options Off Table on Iran Nuclear Program," Reuters, 25 Jan 12.