the expose book Woodward wrote on the Supreme Court.
Woodward once promised to reveal his source upon the source's death. But after several Supreme Court Justices died, he backtracked and said he wouldn't say if any of them was his source, because it might identify someone still alive and on the bench through process of elimination.
There are only two justices still on the court who where there when Woodward wrote The Brethren, and one of those is Rehnquist. Details:
http://www.law.com/jsp/article.jsp?id=1030821212697