Even for a country deep in political turmoil, the killing of Massoud Ali Mohammadi in Tehran today came as a shock. There have been arrests, disappearances and occasional shootings, but the manner of his death was as meticulous as it was disturbing.
Mohammadi was blown up outside his home in an smart northern suburb of Tehran by a remote-control bomb that had been attached to a motorcycle parked on the street. As his stunned neighbours cleared up the rubble they struggled to understand why a little-known academic would have fallen victim to such a highly professional assassination.
The answer may lie in Mohammadi's profession and political inclinations. He was a particle physicist and a supporter of the Iranian opposition movement, raising the possibility he had become the latest victim in a covert war over Iran's nuclear aspirations. It is a war in which scientists find themselves potential soft targets.
Over the past three years, another nuclear scientist has died in mysterious circumstances, and a third vanished without trace while visiting Saudi Arabia last June. In the same period, a former deputy defence minister and general in Iran's Revolutionary Guards also disappeared while on a visit to Istanbul.