As the U.S. and Europe brace for a showdown with Iran over that country’s nuclear program, a former British Customs investigator is asserting that the West missed a golden opportunity to disrupt Tehran’s nuclear effort seven years ago.

Atif Amin says that as a U.K. Customs agent in 2000, he uncovered evidence that Pakistani scientist Abdul Qadeer Khan was running a nuclear black market. But the United States and United Kingdom waited more than three years to take action to shut down the Khan network, which supplied Libya, North Korea and Iran with gas centrifuge technology to enrich uranium.

Had they moved against Khan sooner, Amin believes and some critics agree, Iran might not have as many as 3,000 centrifuges today and be threatening to become a nuclear power.

The previously undisclosed account of Amin’s thwarted investigation is included in a new book about A.Q. Khan titled “America and the Islamic Bomb: The Deadly Compromise” by David Armstrong and Joseph Trento of the National Security News Service. Amin recently sat down with NBC News and discussed details of his investigation, recounted in the book, including his frustration over the decision to limit his criminal probe.

U.S. intelligence officials who worked on the Khan case tell NBC News that Amin’s concerns are misguided.  They say that premature action could have jeopardized secret operations under way at the time targeting Khan, his cohorts and his clients. The officials say that intelligence gained during that period enabled the U.S. to mount other clandestine operations that may still be active, including one aimed at slowing down Iran’s nuclear weapons program.

Amin was tapped to work on what initially appeared to be an export control case involving a suspicious shipment of high-tensile aluminum that could be used to make centrifuge and missile parts. “It didn’t matter who the end user was,” Amin said. “It needed an export license.”

The shipper was a U.K.-based company run by Abu Bakr Siddiqui, a British businessman whose father was a friend of Khan. The stated destination: a company in Dubai, a port that intelligence sources say is notorious for a process in which a shipment is illicitly forwarded to another country. 

T. Mughal / EPA file Abdul Qadeer Khan

Despite a warning from British Customs, Siddiqui shipped the aluminum in May 1999 without obtaining the required license, according to Amin. British Customs intercepted the shipment and searched Siddiqui’s office, home and his parents’ home, he said.

Amin, 30 at the time and a member of a special counterproliferation unit, was assigned to be the case agent. He had worked on several big weapons smuggling cases before, but this was the most daunting assignment of his career. 

During the summer of 1999, he said, he and his team pieced together Siddiqui’s history of shipments and business ties. 

A Sri Lankan 'ran the show'
According to Amin, the Dubai company to which the aluminum was supposed to be shipped was Sama Machinery and Equipment. Amin said he learned that Sama was controlled by one of Siddiqui’s business partners, Buhary Syed Abu Tahir, a Sri Lankan operating out of Dubai and Malaysia. “From a practical point of view,” Amin said, Tahir “ran the show.”

Since Dubai did not have aerospace or nuclear industries that would require the specialized aluminum, Amin wanted to know where the aluminum was really going. “That was really the million dollar question,” he said.

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