Unsurprisingly, the regime is blaming the U.S. and Israel:
A remote-controlled bomb attached to a motorcycle killed an Iranian physics professor outside his home in northern Tehran on Tuesday, state media reported, blaming the United States and Israel for the attack.
But it's not even clear that the scientist, Massoud AliMohammadi, was a nuclear physicist or involved in any way in Iran's nuclear program:
[T]wo Iranian academics, who spoke in return for anonymity because of the sensitivity of the issue, said in telephone interviews that he was not a nuclear physicist and had specialized in particle and theoretical physics. The Web site of Tehran University lists him as a professor of elementary particle physics.
So what the hell. You can't even tell for sure what's going on here. Maybe the regime killed him or they're lying about it being a bomb, maybe it was some anti-regime group, who knows. But I am confident that it'll increase support for the regime in the short term because assuming it was the U.S. or Israel is the natural thing to do.