A fragment of the device was found amongst the wreckage of the jumbo jet Pan Am Flight 103 which exploded over the Scottish town of Lockerbie in 1988, killing 270 people.

Trial details

The two accused are Abdelbaset Ali Mohmed Al Megrahi, 48, and Al Amin Khalifa Fhimah, 44 They deny three charges - murder, conspiracy to murder and a breach of the 1982 Aviation Security Act The trial, in Camp Zeist, in the Netherlands, is expected to last a year About 1,000 witnesses are expected to be called The case is being heard by three Scottish judges

Mr Lumpert had worked for the Zurich-based company Mebo and said he drew up a blueprint for the electronic component in 1985 after the firm's co-owner, Edwin Bollier, came to him with an urgent order.

Two working prototypes were completed and Mr Lumpert, 58, from Switzerland, assumed they were delivered to Mr Bollier's contacts in the East German secret police.

However, the trial at the Scottish court in the Netherlands heard that the East German connection was not mentioned to police and other investigators after the aircraft was blown up in December 1988.

It only came to light in an interview at the Swiss public prosecutor's office in October 1993, three years after his first meeting with them.

Prosecutor Alan Turnbull QC asked Mr Lumpert: "Have you not given thought many times over the years to the question of MST-13 timers?"

Witness quizzed several times after attack

Mr Lumpert replied: "No, not really. I had so many other things had to make I could not concentrate on the MST-13 alone."

Mr Turnbull the asked: "You have only been interviewed in connection with one mass murder in the last few years, have you not?"

"Yes," said Mr Lumpert, who worked for Mebo from 1978 to 1994 but who now works for IBM in Switzerland.

Mr Turnbull continued: "These interviews have all concentrated around the MST-13 timers. Have you not given much thought to your involvement with MST-13 timers?"

"Naturally," he replied.

Mr Turnbull went on to establish there were discrepancies in what Mr Lumpert told investigators about who had been supplied with the MST-13 timers.

Later interviews

Mr Turnbull asked: "In July of 1991 you said that you had no idea to whom Bollier was selling these items. Why did you not say that you thought that they were going to East Germany?"

Mr Lumpert: "Because I couldn't remember it at that point."

The references to East German and Stasi customers only arose in later interviews because he had "remembered all of a sudden" about Mr Bollier's trips to East Berlin after discussing the matter with his wife, said Mr Lumpert.

Describing how he came to devise the MST-13 timers, Mr Lumpert said: "Mr Bollier came to me and said he simply had to have two timers as soon as possible.

"So I worked on that Saturday and Sunday in order to make them ready and after that I found out that he went to the GDR and took the two timers with him."

Part of timer found in aircraft wreckage

Mr Lumpert told the court that he had discussed what he referred to as "the timer problem" with Mr Bollier and Mebo's other co-owner Irwin Meister after it emerged their equipment had been used in the Lockerbie bomb.

Last week, Mr Bollier told the court he sold 20 MST-13 timers to Libya in 1985 and watched Libyan military carry out explosive tests with them at an army base near Tripoli.

The court also heard the Swiss businessman wrote to the CIA shortly after the Lockerbie bombing blaming Libya for the atrocity.

Mr Al Megrahi's defence last week suggested to Mr Bollier that he wanted to deflect attention away from the Stasi, who had allegedly passed on Mebo's MST-13 timers to groups including the Popular Front for the Liberation of Palestine - General Command.

The trial continues.