Iran ? A senior physics professor who publicly backed Iran’s opposition leader was killed when a bomb-rigged motorcycle exploded as he left for work Tuesday. The government blamed the U.S. and Israel for the attack.

The blast apparently was set off by a remote trigger, but it was unclear why the professor was targeted.

The victim was a 50-year-old researcher with no prominent political voice, no published work with military relevance and no declared links to Iran’s nuclear program.