Roshan's death tops a lengthy chronology of events that have targeted the Iranian nuclear program. Late last year, there were three successive, mysterious explosions including one in the city of Isfahan where there is a uranium conversion facility and another at a missile base that killed the head of Iran's ballistic missile program and 16 others. Iran said both were the results of accidents.
A highly complex computer virus known as Stuxnet was also unleashed in 2010 to disrupt Iranian nuclear activities. Again, many cyber security experts have put the U.S. and Israel on a short list of nations thought to be capable of creating the virus.
Wednesday's attack comes during the highest tensions between the U.S. and Iran in decades, perhaps since Iran's revolution in 1979. This month, the U.S. imposed sanctions that bar companies from doing business with Iran's Central Bank and the European Union is discussing sanctions oil exports.
Iran has threatened to close off the Strait of Hormuz if its exports are blocked. The strait sees about one-fifth of the world's oil pass through it.
The head of Iran's military said last week that American naval ships would need their permission to pass through the strait -- an assertion the Pentagon rejected.
ABC News' Lee Ferran and Kirit Radia contributed to this report.