The failure of Iran's Hezbollah paramilitaries to make "a serious attempt to break up" the peaceful reformist student protests over the sentence was thought to be associated with Supreme Leader Khamenei's implicit criticism of the sentence and the "impartiality" of his failing to side with conservative hardliners. - Source
According to Wikipedia, impartiality means "is a principle of justice holding that decisions should be based on objective criteria, rather than on the basis of bias, prejudice, or preferring the benefit to one person over another for improper reasons."
Despite considering the above definition, I have problem understanding the meaning of impartiality in the paragraph. I don't know if it says that the person in question has failed to be impartial, or has been impartial in failing to be side with conservatives. I am puzzled.