Iran faces more politcal intrigue after Massoud Ali Mohammadi, an Iranian physics professor, was killed by a bomb blast on Tuesday.
Tehran has accused the US and Israel of assassinating Mohammadi, who was allegedly linked to their divisive atomic weapons programme.
But the US has rebuffed the accusation. Mark Toner, a US state department spokesman, said it was "absurd" to suggest that the US was involved at all.
Mohammad Khatami, a former president of Iran and a high profile backer of the opposition, wrote on his website that the "ugly face of terrorism" was behind the bombing.
Khantami did not directly accuse any group of the killing, but said the attack was carried out by groups seeking to "further destabilise the crisis".
So who was the assassinated professor? Was he a nuclear scientist supporting the regime as Iran's media claims, or part of the opposition as Iranian reformists allege? And who is responsible for the bomb attack?
Joining presenter Nick Clark are Joshua Goodman, an associate director of the European Foundation for Democracy, Siavush Randjbar-Daemi, a researcher in contemporary Iranian history at the University of London, and Syed Mohamed Marandi, the head of North America Studies at the University of Tehran.
This episode of Inside Story aired from Wednesday, 13 January 2010.
Source: Al Jazeera