The Iranians blame this on domestic Green Revolution dissenters, but targeted assassinations by bombing hasn’t been their style, and this wouldn’t likely have been their target.  Their second accusation in the killing of a nuclear physicist tied to their weapons program sounds more likely:

An Iranian nuclear scientist was killed Tuesday by a remote-controlled bomb planted on a motorcycle parked outside his home, state news outlets reported. Government-controlled media reports blamed the attack on “anti-revolutionary” elements within the country and on Iran’s foreign foes.

Masoud Ali-Mohammadi, described by his colleagues as a non-political person, was killed as he left his house in the north Tehran neighborhood of Qetariyeh. Tehran’s chief prosecutor Abbas Jafari Dolatabadi said Ali-Mohammadi was a nuclear scientist.

The rare bomb attack comes amid tensions between the government and a vocal grassroots opposition movement and international pressure over Iran’s controversial nuclear program, which Tehran says is aimed only at energy production and other peaceful activities but the United States and its allies believe is focused on creating nuclear weapons.

Iran has accused the United States of kidnapping a nuclear scientist who was on pilgrimage in Mecca, Saudi Arabia in May, and of snatching a former deputy minister of defense who disappeared early in 2007 while visiting Istanbul.

Shahram Amiri, the scientist, has been transferred to the U.S., Iran’s foreign ministry said in December. According to U.S. and Israeli media, former defense minister Ali Reza Asgari defected while in Turkey. A senior U.S. official told The Washington Post in March, 2007 that Asgari was cooperating with Western intelligence agencies.

Ironically, the mullahs might get more mileage out of focusing their accusations domestically rather than on foreign efforts.  They desperately need to discredit the Green Revolution movement in order to blunt its spread to the general population.  Tying it to domestic terrorism might just do that, keeping ordinary Iranians on the sidelines and off the streets, as well as giving the mullahcrats a handy death-sentence charge against its organizers.

But really, this had to come from outside, from a nation attempting to stop the nuclear-weapons development that Iran stubbornly insists on pursuing.  The question will be which nation.  The Iranians will blame the US and Israel, but targeted bombings aren’t our style either, except on the business end of a Predator-launched missile.  Besides, can anyone envision Barack Obama giving a green light to such a mission in Iran by granting a waiver of Executive Order 12333?  The Israelis have more experience with this kind of covert action, but the British and French could have carried it out as well.

We may never really know who did it — and that would be the point.  It seems someone has decided to end the nuclear-weapons development of Iran short of open warfare but without wasting time on pointless sanctions proposals that won’t get approval from Russia and China.  Iran won’t have much power to stop a concerted covert war against its scientists without arresting them all and forcing them to live in the laboratories, which won’t exactly be a morale booster.