IT may have not been clear up to now, but I think this kinda settles it:

A bomb attached to motorcycle killed an Iranian professor of nuclear physics outside his home in northern Tehran on Tuesday, the state-run Press TV broadcaster reported on its Web site.

The authorities called the killing of the scientist, Massoud Ali Mohammadi, an assassination carried out by terrorists, but did not say who was believed to be responsible. The professor taught neutron physics at Tehran University, Press TV said, but it was not clear whether he was part of Iran’s contentious nuclear enrichment program.

Why do you think he was blown up, then?

The WSJ points out that "[t]error attacks against Iranian officials and targets in remote provinces aren't uncommon. But a bombing in Tehran, the capital, is extremely rare, and the target -- a nuclear scientist -- raised immediate questions over whether the attack was related to Iran's controversial nuclear program."

UPDATE. Here's a new twist:

State media identified the victim as Masoud Ali Mohammadi, a professor at Tehran University, which has been at the center of recent protests by student opposition supporters. Before the election, pro-reform Web sites published Mohammadi's name among a list of 240 university teachers who supported Mousavi.