The three-year investigation had led the FBI to conclude that Iran was involved in the attack. At that time, the Clinton administration hoped to open a dialogue with reformist president Khatami, which would be impossible after accusing Iranians of supporting terrorist action. A secret letter, delivered directly to Khatami by Sultan Qaboos of Oman, stated that the United States had evidence of direct Iranian involvement in the act, and demanded that those involved be held responsible for their actions. Khatami refused to begin an investigation and Iranian officials stated that al-Qaeda was responsible for the attack.