Killed in Iran: Part of a Nuclear Trifecta Iranian security forces inspect the site where a magnetic bomb attached to a car exploded in Tehran Wednesday morning, killing an Iranian nuclear expert It has been a busy day or so on the nuclear front: An Iran nuclear scientist was assassinated Wednesday morning in Tehran. The Bulletin of Atomic Scientists moved its Doomsday Clock warning of nuclear war to 11:56 p.m. - one minute closer to the midnight when it believes nuclear war could break out. And the Nuclear Threat Initiative released its Nuclear Materials Security Index, a database charting publicly for the first time 32 nations that possess the fissile guts of nuclear weapons - and how secure they are. The trio consists of three discrete elements, but - like a radioactive Venn diagram - they overlap in disconcerting ways. "There is evidence today that the elements of a perfect storm are in place: an ample supply of weapons-usable nuclear materials - some of it poorly secured - and the determination of terrorist organizations that have publicly stated their desire to acquire and use nuclear weapons," says former senator Sam Nunn, co-chairman of the Nuclear Threat Initiative." NTI, which developed the index with help from the Economist Intelligence Unit, associated with the British magazine of the same name, believes that making information about securing nuclear materiel public will encourage tighter controls. It's plain that's one of the reasons why the folks at the Bulletin of Atomic Scientists are increasingly nervous. The minute hand on their Doomsday Clock was set at 11:58 in 1953 at the height of the Cold War; after moving several times since, it was set all the way back to 11:43 in 1991 after Washington and Moscow inked the Strategic Arms Reduction Treaty. But a lack of global progress on nuclear weapons since then has allowed the hand to tick closer to midnight; after rumbles of never-realized arms-control progress two years ago, BAS moved the hand from 11:55 to 11:54. "Two years ago, it appeared that world leaders might address the truly global threats that we face," the organization said in a statement announcing the latest change. "The path toward a world free of nuclear weapons is not at all clear, and leadership is failing," says Jayantha Dhanapalaa, a BAS official who served as the UN's undersecretary-general for Disarmament Affairs from 1998 to 2003. The world still has over 19,000 nuclear weapons, enough power to destroy the world's inhabitants several times over. But nuclear weapons remain the crack cocaine of world leaders, crazy or not, who want the security they seem to offer. And those who fear such weapons falling into what they deem to be the wrong hands are just as determined to see they don't get them. That certitude is apparently behind the killing of Mostafa Ahmadi Roshan, a 32-year old Iranian chemist. He died after an unknown killer, riding a motorbike, affixed a bomb to his gray Peugeot 405 in northern Tehran that exploded moments later. "The bomb was a magnetic bomb and is the same as those previously used to assassinate scientists," Tehran Deputy Governor Safar Ali Baratlo said, "and is the work of the Zionists." Both Israel and the U.S. have denied involvement in such attacks. Ahmadi Roshan was skilled at developing the sophisticated membranes critical to enriching uranium to weapons-grade levels. Apparently his killer's overlords knew who he was, and how vital he was to Iran's nuclear ambitions. They also know that killing such key scientists - Ahmadi Roshan is at least the fifth to die in recent years - can snuff out the chain reaction that could lead to a Persian nuclear bomb. "Global nuclear security," Nunn said as he unveiled his organization's new index, "is only as strong as the weakest link in the chain." Nunn was speaking defensively, of course. But someone in Tehran Wednesday morning felt that offensive action was required.