Although the Iranian regime has blamed the United States and Israel for the "heinous act," whoever perpetrated this murder was no friend of the U.S. This mishap occurred in the wake of Secretary of State Hillary Rodham Clinton's call on Iran "to return to negotiations with the P5+1," the five permanent members of the United Nations Security Council plus Germany. The statement deplored Tehran's decision to start uranium enrichment at a bunker facility in Fordow, but it reiterated that the goal of U.S. policy is "reaching a comprehensive, negotiated solution that restores confidence in the exclusively peaceful nature of Iran's nuclear program." The assassination clearly undermines this objective.

Mostafa Ahmadi-Rowshan with his son / Farsnews

Notwithstanding Secretary Clinton's immediate reaction to the assassination by categorically denying "any United States involvement in any kind of act of violence inside Iran," Tehran blamed the bombing on "America and the criminal Zionist regime." A disturbing saying, fueled by livid nationalism, spread across Iran like wildfire, "They save our sailors, but kill our scientists." The phrase refers to the humanitarian-cum-diplomatic rescue operations by the U.S. navy in the Persian Gulf that has saved the lives of Iranian mariners in the past few days. The goodwill gesture that countered Iran's threats to close the Strait of Hormuz to global oil traffic has been largely ruined by the coldblooded murder.

This is the fourth Iranian scientist who has been mysteriously murdered in the past two years. Such acts of terrorism are unlikely to significantly delay or deter Tehran's nuclear program. It is implausible that Iran's expansive cadre of nuclear scientists depend on one or several individuals. Most of these scientists were educated at Iranian universities and are thus replaceable. Rather, it is the adverse effects and ramifications of these terrors that are most likely to be felt outside of Iran.

The resulting climate of insecurity feeds ammunition to hardliners in Tehran demanding reprisals. Fereydoun Abbasi-Davani's appointment as the new head of Iran's atomic energy organization may have been part of the backlash against the campaign to eliminate Iranian scientists. Abbasi, suspected of involvement in Iran's alleged nuclear weapon program and blacklisted under UN sanctions, survived a near-identical assassination attempt in November 2010. It is now under his watch that Iran tips closer toward becoming a nuclear weapons threshold state.

The growing battery of dark art attacks against Iran's nuclear program -- assassinations, sabotage, and cyber-attacks -- is likely to further diminish Tehran's cooperation with the International Atomic Energy Agency (IAEA). Iran claims that Rowshan became a target after he was interviewed by international nuclear inspectors. A few weeks from now, representatives from the IAEA are scheduled to visit Iran, a trip aimed at resolving some of the outstanding issues between Iran and the agency. Wednesday's killing gives the Iranian government an excuse to stonewall access to its scientific community and subvert the agency's efforts. If the IAEA loses some of its access, the world will have markedly less information about Iran's nuclear program, which will make the goal of taming Iran's atomic ambitions more difficult.