Apparently he had become more and more angry about the current government and was set to "leave". This anyway is the rumor making the rounds. Should he has considered (or been considered by some overly zealous "defenders" of the government) leaving--- as a number of scientists have over the past few years--- he'd have been a propaganda prize, albeit quite minor, in the bonnet of the west and not a threat. Little about his "know-how" nor subjects make him interesting as a target for the west except as yet another voice in support of the opposition. For Iran's government, however, he is a good example to set.
Ashley Madison says Noel Biderman is stepping down as CEO of Avid Life Media Inc. (Reuters)
from the article: ANALYSIS / Iran scientist likely killed by opponents of nuclear program