So I just spoke with one of Eliot Spitzer's top aides, Sean Patrick Maloney, who, along with another staffer, was named “special counsel” right around the time when the attorney general’s investigations into the governor’s office began. According to this story in the New York Post, the appointments may have been intended to thwart the investigation into whether other aides to the governor tried to use the state police to gather travel information about Senate Majority Leader Joe Bruno.
Maloney, a lawyer who worked in the White House in Bill Clinton’s second term, said that in fact, his new title didn’t provide him any kind of shield. He said that there’s no such thing as after-the-fact attorney client privileges, meaning that he was, and still is, available to be questioned about anything he knew before he became a "special counsel." (He has yet to be questioned by investigators.)
For what it’s worth, Maloney’s assessment squares with that of one legal expert I spoke to , who said that the only privileges that apply retroactively are marital ones. (A wife can't be forced to testify about any conversations she had with her husband, ever, no matter when they got married.)