|Urs Tinner (pictured) and his brother and father are suspected of being linked to the AQ Khan network [EPA]
A Swiss magistrate has said three engineers suspected of giving nuclear weapons to the Khan network in Pakistan should face smuggling charges.
Andreas Mueller, the magistrate investigating a six-year federal inquiry into an alleged smuggling ring, said his report on Thursday was based on an exhaustive investigation.
"There are many parts. It's like a puzzle and if you put the puzzle together you get the whole picture. There is not [just] one piece of evidence, there are many pieces of evidence," he said.
Swiss engineers Urs Tinner, his brother Marco and their father Friedrich are suspected of having maintained links to the nuclear-smuggling network led by Abdul Qadeer Khan, the creator of Pakistan's atomic bomb.
But the trio have maintained their innocence, saying that they worked as spies for the CIA and exposed Libya's nuclear ambitions and topple Khan's smuggling network.
Mueller said the Tinners did not deny working for the Khan network, but claimed they did not know his aim was to produce nuclear weapons. He also said the Tinners had worked for the CIA since June 2003.
The case into the alleged smuggling ring was slowed down after the Swiss government repeatedly ordered evidence destroyed, allegedly under pressure from senior US officials.
In June 2009, the Swiss government ordered the destruction of about 100 pages of evidence linked to Mueller's investigation of the Tinner family, saying they contained information that could have endangered national security and needed to be kept out of "the wrong hands".
The cabinet said those documents were "the most explosive'" material in the case's file of more than 1,000 pages.
The documents are copies of files destroyed in 2007 under a previous order that led to protests from lawmakers and legal experts, who said the government had undermined the prosecution in the smuggling case.
The copies were found in prosecutors' archives in December 2008.