Shahram Amiri went missing in 2009 after leaving for a pilgrimage to Mecca, but appeared in a video - apparently recorded in the USA - in which he claimed to have been put under pressure to 'reveal sensitive information' to the intelligence agency.
He then walked into the Iranian interests section at the Pakistani Embassy in Washington and demanded to be sent home. He came back to a heroes welcome and insisted he was a 'simple researcher'.
Amiri worked for a university affiliated with Tehran's extensive nuclear program. He is said to have had an in-depth knowledge of Iran's nuclear programme and was kept at a secret location after returning to the country.
According to CBS, he told officials in interviews he was being held against his will by Saudi and U.S. spies.
But American officials said he was set to receive millions for the information.
Amiri's mother told the BBC that his body had been sent to her with rope marks around his neck.
Today, an Iranian judicial spokesman confirmed the execution had taken place.
He told the Mizan Online news site: 'Shahram Amiri was hanged for revealing the country's top secrets to the enemy (US).'