Lee was fired last March from his top secret research job at the Los Alamos laboratory in the United States - a post he held for 20 years - amid a widening probe into suspected mainland espionage. He was indicted last month.

The 59 charges involve the illegal downloading of some 806 megabytes of weapons design, testing and construction information - offences that, while not constituting espionage, still carry the threat of life imprisonment. The prosecution now claims the material - around 800,000 pages worth - is enough to 'change the world's strategic balance' but are clearly no closer in determining his motives.

'Lee is clearly in their sights, despite the fact that elements of the investigation have been farcical,' said one foreign diplomat familiar with the case. 'It seems they are just not going to let this go, however bungled things were early on. This looks like it is going to get very, very ugly given all the uncertainty.' The espionage link was spelt out in an Albuquerque court last week by FBI Special Agent Robert Messemer, an expert in Chinese intelligence. Just as US District Court Judge James Parker was reportedly considering freeing Lee in the interim under considerable restrictions and 24-hour FBI surveillance, Mr Messemer played the national security card.

All manner of signals could be used to alert foreign spies that Lee was prepared to dispatch seven missing computer tapes full of downloaded secret data, Mr Messemer suggested. In open court, Mr Messemer attempted to document on behalf of the prosecution a 'pattern of deception' dating back to 1982 when he called a colleague at the Lawrence Livermore lab under investigation for spying to offer assistance.

He claimed it continued through trips to Beijing on lab business in 1986 and 1988 with one 'clandestine' meeting in a hotel room finally revealed under questioning last December.

Then there was the case of a link to Zheng Shaoteng, the head of China's Institute of Applied Physics and Conceptual Mathematics. Lee had always insisted he had received nothing more than a Christmas card from Mr Zheng, one of the mainland's foremost scientists.

Mr Messemer claimed FBI agents searching his garage last April after his sacking found a request for certain unclassified information.

The tapes themselves also form a key part of the prosecution drive to keep the softly-spoken Lee firmly behind bars until any trial despite his plea of not guilty. Lee's defence lawyers insist the tapes have been destroyed. The prosecution insists there is no evidence that they do not exist and in the interim are keen to raise fresh doubts.

Mr Messemer testified that the risk of their falling into foreign hands had now intensified. Hostile forces now knew of their existence and would be trying to get them from Lee - a claim his lawyers described as 'ludicrous'.

They also said he deleted information from at least two tapes when he discovered he was about to lose his security clearance.

Fellow ethnic Chinese scientists working in the labs now say they are 'terrified'.

'He has apparently committed serious breaches of security but he is not the first,' one veteran of Lawrence Livermore said.

'That is one thing and if he is guilty, then he should face the music. But the vicious way they are painting him to be a spy when they can't make up their minds if he was working for China or Taiwan is quite evil.

'They will do whatever they can to get him and save face for the Justice Department, the Energy Department and the FBI.

'We are watching a witch-hunt unfold. It is terrifying.' Greg Torode is the Post's Washington correspondent