Could be Mossad...but then again there are numerous other nations in the mideast which don't want Iran to have nukes, All the Sunni led countries for instance, and any ME country that doesn't want to be thrteatened and plundered.. Saudi Arabia has already said they would have to get nukes for themselves, if Iran did.
It would be far easier for a fellow Muslim intel agency to infiltrate Iran than it would be for Mossad to do so. It seems a Sunni led country and intel agency could fairly easily find a discontyed Sunni in Shiite dominated Iran.
Just some 'food for thought'.