Mannheim: The trial of a German engineer accused of aiding Libya's nuclear programme collapsed on Wednesday.

The presiding judge complained that documents had been withheld from the court.

Gotthard Lerch, 63, went on trial in March, charged with breaking German export and weapons laws for allegedly helping supply uranium-enriching equipment to Libya between 1999 and 2003. Libya has since abandoned its nuclear programme.

Judge Michael Seidling, calling a halt to proceedings at the Mannheim state court on Wednesday, said that prosecutors and investigators had possessed documents "about which the court knew nothing."

That, he said, raised doubts about whether the trial could proceed fairly.

The prosecution argued that Lerch played a key role in the network of Pakistani scientist A.Q. Khan and supplied Tripoli with sensitive technology in the full knowledge that it was seeking atomic weapons.

Lerch had denied the charges.

In another setback to prosecutors, Germany's highest court already has questioned the credibility of a key witness, a Sri Lankan businessman who is also a suspect in the case.

Lerch was arrested in Switzerland in 2004 and extradited to Germany last year. The Mannheim court was expected to decide on Wednesday whether to free him from custody.

Judge Seidling said that slow handling of requests to other countries for legal assistance had also complicated the trial.

Such requests were made to Switzerland and Liechtenstein, among others.

Prosecutor Peter Lintz said that problems at the trial had resulted from the scale of the proceedings.