A news item last week from Tehran gives some insight on the complicated Iranian domestic political scene.
A Tehran University professor of physics, named Masoud Ali Mohammed, was killed near his home by a large remote-detonated explosion. The Iranian news reports claimed that the deed was done by Israelis, Americans, and internal enemies of the government. The presumption in that allegation was that Mohammed was engaged in vital research toward the development of Iran's nuclear capability, and that thus Israel/US interests were served by taking him out.
Implicit in that report is that Iran is actually doing anything with nuclear power that would threaten Israeli/American security (although an imaginative liar could probably stretch the truth so far as to say that it would be some sort of threat what they did with peaceful nuclear energy).
The plot thickens with the added detail (from acquaintances of the deceased) that he had encouraged his students to participate in Green demonstrations against the Iranian regime. Also, that his specialty is quantum theory.
These two facts give the lie to the Iranian allegation--there is very little of theory involved with the production of nuclear weapons these days; it's about the technical details of centrifuges, collecting the enhanced uranium, and creating the proper physics to detonate it.
So, the strategy by the Iranian perpetrators is to eliminate a prestigious opponent that could somewhat plausibly be identified as a possible target for foreign spies.
I would suggest that even if Mohammed were involved in research more vital to Iran's nuclear weapons program, it might have made sense to kill him off as a political enemy of the regime. Their long-term strategy, it would seem most likely, is to move all the way to the verge of deliverable nuclear warheads--not actually to use them (a move which would be suicidal). The run-up to that stage gives great opportunities to try to extort concessions from the West, so it should be prolonged.
Iran has reneged on all forms of the proposal to exchange their enhanced uranium for better-quality, non-weapons-grade material (after what appeared to be a pretty active internal debate). It is time to apply stiffer sanctions on Iran, particularly ones aimed at the individuals heading the administration and military, so that they don't see this blackmail opportunity phase to be so enjoyable.