A Sri Lankan businessman who helped Pakistani scientist Abdul Qadeer Khan build a secret international network for supplying nuclear material and equipment was arrested by Malaysian police on Friday for threatening national security, officials said.

Police detained Buhary Syed Abu Tahir three months after they released a report, based largely on his interrogation, detailing how Khan provided Libya with enriched uranium and equipment that could be used in developing weapons and how he provided Iran with components for its nuclear program.

Though Malaysian police said in February that Tahir had committed no crime, they are holding him under the country's internal security act, which allows suspects to be detained without charges or trial, Malaysian officials said.

Police had opened the investigation after U.S. and British intelligence agents informed local authorities late last year that Malaysian-manufactured parts for building centrifuges used in making weapons-grade uranium had been found aboard a German-owned ship bound for Libya. The discovery proved to be a major breakthrough in efforts to unravel Khan's network.

Tahir remains a central figure in the investigation along with two other alleged Khan associates -- Swiss engineer Friedrich Tinner and British businessman Peter Griffin. All three have been scrutinized for possible arms proliferation activity at various times over more than two decades.

In 1980, following complaints from the United States, Swiss authorities examined a company where Tinner was export director for possible violations of export laws in the sale of industrial valves to Pakistan's nuclear program. Neither he nor the company, which he left, was charged with any crime. Swiss officials said this year that they had opened an inquiry into a Tinner family company concerning alleged dealings with Khan, in light of information provided by Malaysian police.

Griffin, who allegedly collaborated with Tahir in drawing up plans for a machine shop to manufacture centrifuge components in Libya, was the subject of a British investigation in the 1970s into alleged business ties with Khan, then one of the leaders of Pakistan's nuclear research program.

Investigators now believe Khan built his nuclear trading scheme around essentially the same network of foreign middlemen and manufacturers that he began assembling three decades ago to circumvent restrictions on sensitive technology that Pakistan needed to build a nuclear bomb.

Tahir's association with Khan dates to 1985, when Tahir took over the management of a Dubai-based family business, SMB Group, and secured a contract to sell air conditioners to Khan's research lab, according to a Malaysian police report. The report said he subsequently moved to Malaysia, where he married a diplomat's daughter and invested in several successful businesses, forging partnerships with, among others, the son of the current prime minister, Abdullah Ahmad Badawi.

Tahir became involved in Khan's proliferation network in the mid-1990s. He helped Khan organize the shipment of centrifuge components from Pakistan through Dubai to Iran, for which Khan was given two briefcases filled with $3 million in cash, according to the account Tahir gave investigators.

A senior Malaysian government official said Tahir was seeking to build a cover for nuclear-related activities in the country by developing relationships with credible business people so he would be seen as having clout and money.

By 2001, however, that cover was beginning to fray when a trial in London's Southwark Crown Court cast light on Tahir's role in procuring restricted equipment for Khan's laboratory.

The accused in the trial was not Tahir but Abu Bakr Siddiqui, his friend and partner in a thriving London-based import-export business that dealt mostly in microelectronic parts, according to Siddiqui's attorney, Andrew Trollope. The prosecution established that Siddiqui was also personally acquainted with Khan, a family friend whom he reverently addressed as Doctor Sahib.

In 1999, Khan asked Tahir and Siddiqui to arrange several shipments of equipment from Britain, according to information made public at the trial. The shipments included a 12-ton heat treatment furnace, a high-specification measuring machine, an overhead crane and high-strength aluminum bars. The customers were listed on shipping papers as Peoples Steel Mill in Karachi and UETC in Islamabad, and Tahir provided a false end-user certificate, according to Trollope.

Siddiqui admitted that the order was outside the normal course of business, but he said he didn't think there was anything wrong or suspicious about it, Trollope recalled.

Prosecutors argued that the equipment had been destined for Khan's lab, producing papers taken from Siddiqui's office showing that he had taken instructions not only from Khan but also from Mohammed Farooq, a senior scientist at the lab who has been under investigation in Pakistan for his alleged role in the proliferation scandal. In the end, the jury convicted Siddiqui on three of seven of the charges, although the judge determined that he had not been aware of how the components would be used. Siddiqui was fined $8,700 and given a suspended sentence.

Tahir was not charged, probably because the government thought there was insufficient evidence, and he never appeared at the trial, Trollope said. Customs officials and prosecutors declined to comment on the case.

It is unclear whether the Siddiqui case alerted Western intelligence agencies to Tahir's involvement in proliferation. The Siddiqui-Tahir link was reported by the National Security News Service, a Washington-based nonprofit organization. U.S. officials have said the CIA had been watching the Malaysian plant that manufactured centrifuge parts for an unspecified period before the seizure of the ship bound for Libya.

Siddiqui was not at his home in West London when a reporter visited on two occasions this year. His brother, who lives on the same street, said Siddiqui was on a short vacation with his family and, in any case, did not want to comment.

Tinner's name surfaced most recently in connection with a Malaysian conglomerate, Scomi Group Berhad, which had been partly owned by Tahir. In a statement to Malaysian police earlier this year, Tahir identified Tinner as a key middleman who had prepared certain centrifuge components, including safety valves, and routed the equipment to Libya through Dubai, according to the Malaysian police report.

Tinner's son, Urs, was hired by Tahir as a technical consultant to set up a Scomi factory in Malaysia and was actively involved in manufacturing operations there, Malaysian police said. Machines for the plant were supplied by a Swiss company, Traco, owned by Tinner's son Marco, according to the report.

In a recent interview in Haag, the village where the Tinners live in northeastern Switzerland, Urs Tinner said his family had committed no crimes and described the investigation as a lot of smoke and no fire.

Standing at the door of the family home, within sight of a stunning, snow-dusted cliff, Tinner, 39, said he was a mechanic and had gone to Malaysia on other business when he was asked to set up the factory operation. He was not in administration, he said, and had no idea what the parts the factory was making were for. It is common in his industry, he said, to simply build things to specifications that a client provides.

He said the machines his brother provided were low-tolerance models that needed no export permission. His father, he said, had been retired for several years and had no role in recent dealings by the family firm.

Another alleged partner in the scheme to sell centrifuges to Libya was Griffin, 68, an engineer from Swansea in South Wales.

Griffin's association with the Libyan program appears to date to June 2000, when he set up a company in Dubai called Gulf Technical Industries. A year later, Tahir helped establish Scomi Precision Engineering, a subsidiary of Scomi Group Berhad.

A Scomi official confirmed that parts, described by police as centrifuge components, were produced for shipment to Gulf Technical Industries. The official, who spoke on condition of anonymity, said it was the first of two shipments by Scomi to Dubai. The second went to Aryash Trading Co., according to police.

Griffin's alleged association with the project did not end there. According to the Malaysian police report, he supplied a lathe to Libya for a project to make centrifuge components that could not be obtained outside Libya. He then arranged to send seven or eight Libyan technicians to Spain twice, to take courses in how to operate the machine, according to the report.

Griffin's son, Paul, has since taken over Gulf Technical Industries. Paul Griffin's lawyer in Dubai, Chris Mills, said the Malaysian report came as a surprise to Griffin, who is now trying to determine how his name became linked to the investigation.

Peter Griffin is retired and living in a villa in southern France. Reached by phone, he declined to comment on the investigation except to say that a statement would be forthcoming. He referred to his relationship with Khan as an "alleged association."

Correspondent John Burgess in Haag, Switzerland, and staff writer Joby Warrick and staff researcher Robert E. Thomason in Washington contributed to this report.