In the dispute over Tehran's nuclear program, the U.N. Security Council has imposed new sanctions. Is Iran truly building a nuclear bomb as Western countries claim? Or are countries playing up the dangers to bring Iran to its knees? Spiegel traces the history of Tehran's nuclear program - with stops in Washington, Vienna and Isfahan.

Editor's note: The following article from this week's issue of SPIEGEL on the origins of Iran's nuclear program will run in two parts. Part I is feature below, and Part II will be published on Friday.

It is yet another of those secret meetings at the International Atomic Energy Agency (IAEA). The deputy director general of the agency, who works on behalf of the United Nations to prevent nuclear bombs from getting into the wrong hands, has invited 35 diplomats to a meeting on the fifth floor of the UN building in Vienna. Some take pictures with their mobile phones of the ice floes on the Danube River drifting by below. Everyone is prepared for a routine meeting. But everything will be different this time. With the help of high-tech espionage, history is written on this February day in 2008. And perhaps it will later be said that it was the day Iran finally lost its innocence, and the day the Israelis were provided with arguments for a war.

Olli Heinonen confronts the diplomats with new information about Tehran's nuclear program. The Finnish nuclear scientist, the IAEA's deputy director general and head of the Department of Safeguards, has been to Natanz and Isfahan several times himself, and his inspectors, or "watchdogs," report back to him regularly. In addition, cameras monitor nuclear activities in many of the Iranian facilities. As useful as all of this is, it doesn't replace supplementary, secret information.

Heinonen knows that there are many things happening in Iran that he doesn't know about. Nevertheless, he has received critical information through indirect sources, including recordings made by a leading Iranian nuclear scientist.

A Treasure Trove of Facts

Always wary of attempts to manipulate him, Heinonen has spent a lot of time comparing the exclusive information with his own records and checking it against other reports. His research has led him to conclude that he has been given a treasure trove of facts, images and names - all of it "with a 90-percent likelihood of being authentic."