The Associated Press
By HANSPETER HAEFLIGER
The documents formed part of a case against three members of the Tinner family who are suspected of involvement in the nuclear smuggling ring of Abdul Qadeer Khan, a key figure in Pakistan's atomic weapons program. Khan has admitted selling nuclear arms technology to Iran, Libya and North Korea.
Couchepin said federal prosecutors discovered that the information contained in the files could be "explosive" for Switzerland's national security.
"There were detailed construction plans for nuclear weapons, for gas ultracentrifuges to enrich weapons-grade uranium as well as for guided missile delivery systems," Couchepin told reporters in the Swiss capital, speaking publicly on the matter for the first time.
Couchepin said the decision to destroy them was taken to prevent the documents getting "into the hands of a terrorist organization" or a rogue state.
He did not comment on the potential impact the destruction of evidence could have if the defendants are ever brought to trial, but implied only that the security and international policy risks were too great to permit its continued existence.
The documents were destroyed under the observation of the U.N.'s International Atomic Energy Agency, he said. The government in November ordered the files to be destroyed, but did not make the decision public at the time.
Couchepin, who holds Switzerland's yearly rotating presidency, read out a prepared statement and declined to answer questions about the case.
His appearance followed a week of media reports that the files were secretly ordered destroyed by the government last year after pressure from the United States, which was concerned that its efforts to clamp down on nuclear smuggling might be compromised.
The U.S. declined comment. "The embassy does not comment on intelligence issues," spokeswoman Lisbeth Keefe said.
The documents were among those seized from the Tinners in the course of a government investigation that started in October 2004.
Prosecutors allege that Urs Tinner, who was arrested in 2004, oversaw machine work in Malaysia on gas centrifuge parts that were intercepted by Western intelligence services. Gas centrifuges are needed to enrich uranium for use in nuclear weapons.
Marco Tinner, whose Swiss-based company reportedly sold equipment to the Malaysian firm that manufactured the parts sent to Libya, is being held alongside Urs in investigative custody.
Friedrich Tinner, their father who has admitted knowing Khan since the 1970s, was released earlier this year.
All three are being investigated on suspicion of violating export laws on controlled goods and war materials. A trial date has not been set.
Associated Press writer Frank Jordans in Geneva contributed to this report.
