Strong Leads and Dead Ends in Nuclear Case Against Iran

The missile modifications, at first thought to have been based on a North Korean design, are now believed to be the handiwork of Iranian engineers. "This clearly wasn't done by the A-team of Iran's program," said one nuclear expert who has analyzed the documents. "It might have been given to an outside team or subcontracted out as an assignment or project for the military, though."

The laptop also includes 18 different attempts to perfect the size, weight and diameter of the nose cone in ways that could accommodate an implosion device. There are accompanying scientific notes describing experiments in the detonation of conventional explosives, suggesting to Western analysts that the author was working through the steps required to compress uranium into a critical mass for an atomic explosion.

"It's not hard evidence, but if you want to bring a building down, you don't need this kind of detonation," said one investigator. "So it's either for missiles or for a nuclear detonation."

In a recent meeting with IAEA inspectors, Iranian officials -- who learned 14 months ago that the United States had the documents on the laptop -- dismissed accusations that they reflect planning for a weapons program.

The Khan Network

In a brightly lighted office at police headquarters in the Malaysian capital, Bukhary Syed Tahir sat down recently for his second round of talks with CIA officers since his arrest 20 months ago on the streets of Kuala Lumpur.

Tahir is held in a high-security prison, without charges, for his alleged role as a manufacturer, salesman and partner in Pakistani scientist Abdul Qadeer Khan's nuclear network, which supplied materials to Libya, Iran and North Korea. After more than a year of denials about shipments to Iran in the 1990s, Tahir has changed his story and now claims to have recalled a previously forgotten sale, according to U.S. sources.

In addition to supplies Iran purchased from the network in the late 1980s to begin its nuclear program, Tahir said, Iran was sent in the mid-1990s three advanced, Pakistani-made centrifuges that could be used as models for manufacturing more. Thousands of properly constructed and assembled P-2 generation centrifuges could improve Iran's ability to make bomb-grade uranium. If the P-2s exist in Iran, as Tahir asserted, intelligence officials said the centrifuges could shorten the time needed for Iran to build a weapon.

Iran has told inspectors that it received only drawings of the P-2s, not the centrifuges themselves, and that it did not build any. A recent IAEA report determined that Iran has not been forthcoming on the P-2s or its dealings with Tahir and Khan, who led Pakistan to nuclear success.

Two sources with direct knowledge of Tahir's recent claims said they did not know what led him to offer a new account. They had no information on whether his new claims were made under duress or came after promises of release.

"Some of the individuals involved" in supplying Iran's program, "like Tahir, provide different accounts at different times, which only adds to the confusion," said a Bush administration official.

A 1987 meeting in a dusty Dubai office kick-started Tehran's nuclear efforts and a side business for Khan that made him rich and ultimately infamous. Iran, at war with Iraq then, bought from Khan centrifuge designs and a starter kit for uranium enrichment. The package included instructions for shaping uranium metal into "hemispherical forms," a process that has no other known use except to shield the core of a nuclear bomb.

"I haven't heard -- even from defenders of Iran -- an explanation for a peaceful purpose, that's not a weapons-related purpose," for the uranium metal, a U.S. official said. Iran contends that the uranium metal instructions were thrown in as a freebie and never used.

Khan, who is under house arrest in Islamabad, Pakistan, has provided few details to U.S. intelligence through his Pakistani handlers.

With Khan's help, Iran spent much of the 1990s secretly constructing a facility, partially underground, to house 50,000 centrifuges that it planned to build. That facility in Natanz is the only such known plant, and U.S. intelligence considers it unlikely that Iran has a hidden duplicate. Natanz was exposed in August 2002, at a time when the Bush administration was building support for war with Iraq. The revelations launched an investigation that took IAEA inspectors through Natanz for the first time three years ago this month.

Since then, they have uncovered matters of concern large and small. Some, such as traces of highly enriched uranium once feared to have been produced by Iran, are now known to have come from Pakistani equipment. Others areas of interest include suspicions of military involvement in uranium mining and plutonium tests.

But the history of Iran's P-2s, the laptop documents and the metal casting stand out as the most troubling for IAEA inspectors, the U.S. government and its allies.

For two years, the White House has sought to convince allies of Iran's guilt. "They say, 'Yes, we agree Iran's activities violate treaties, and, yes, it does seem like they are interested in nuclear weapons,' " a senior administration official said. The differences still to be worked out, between Washington and the world, are over "the proper course of action," the official said.

Researcher Julie Tate contributed to this report.