In the 15 months since Libya turned over to the United States nearly two tons of illicit uranium it had planned to use in atomic weapons, the radioactive material has become a pivotal, if mysterious, piece of evidence for investigators unraveling the nuclear black market.Logic suggest that it is unlikely that an empty crate made for uranium would be transported from North Korea to be filled elsewhere. And even if for some weird reason it was, the Norks were still guilty of conspiring to assist in the proliferation of nuke weapons.
The Bush administration, joined by United Nations inspectors, now say the uranium most likely came from North Korea and helps to build a case that the North has exported dangerous nuclear material to Libya, and perhaps beyond. The officials drew on scientific tests, secret documents and interviews with key players in the black market, which taken together are potentially highly incriminating. But the evidence is also circumstantial.
In interviews this week, administration officials and foreign diplomats disclosed that Libyan officials had also surrendered financial ledgers to the United States that provide a guide to the front companies involved in the nuclear network set up by Abdul Qadeer Khan, the Pakistani scientist. One large payment, American officials contend, was directed to North Korea, presumably for the uranium hexafluoride that arrived in Tripoli in 2001. But American and foreign officials who have seen the financial documents or been briefed on them say they do not prove a direct payment from Libya to the North Korean government.
Yet Iraq haunts the American effort to lay out its case on North Korea. In their often-contentious strategy sessions with China and South Korea, American officials have found themselves confronted by the question: why should Washington be trusted now?
The tale of the uranium found in Libya is a case study of the trouble in filling in that map of the nuclear world. But it is also a very different story from what happened in Iraq, where there were bitter fights about whether Saddam Hussein was building dangerous stockpiles. Here, the questions are who made the uranium that was found in Libya, who sold it, and is there more?
The story began in late 2003, when Libya surrendered its nuclear program and led American, British and I.A.E.A. officials to the cask of uranium. It was flown to Washington in early 2004. In February 2004, Malaysia published a report - based on interviews with Buhari Sayed Abu Tahir , the chief operating officer of Mr. Khan's network - that the uranium hexafluoride had been flown to Libya aboard a Pakistani airplane in 2001. The findings of the Malaysian report, and the involvement of the Khan network in the uranium shipment, were widely reported.
News of a possible North Korean link to the shipment emerged last spring when European investigators, quoted in The New York Times, said their interviews with members of the Khan network had pointed them in that direction.
Meanwhile, American officials also began to suspect North Korea was the source, partly because chemical traces on the outside of the cask indicated that it had been at the North's main nuclear site, Yongbyon. The United States had plutonium samples from that site. But as one American official said, "proving the container had been there is different from proving that the uranium inside it" also came from North Korea.
Joseph Cirincione, director of the nonproliferation project at the Carnegie Endowment, said the traces of plutonium might simply indicate that North Korea shipped an empty canister to Pakistan, and that it was filled there, or someplace else. "If you look hard at these pillars, there are alternative explanations," he said. "They don't disprove the government claims but they raise doubts about their certainty."