He made his name with Fatal Vision, about Green Beret physician Jeffrey MacDonald, who was convicted of killing his wife and children. MacDonald gave McGinniss full access to himself and to his defense, believing that McGinniss would write a favorable account of his case. During the time he spent with MacDonald, McGinniss concluded that MacDonald was in fact guilty of the murders, but led MacDonald to believe that he thought MacDonald was innocent so as not to lose access to him. Fatal Vision wound up being a total hatchet job on MacDonald.
Having read Fatal Vision, I think McGinniss made a strong case for MacDonald's guilt, but I'm not totally convinced because of McGinniss's own credibility problems and lack of honesty.
I recall reading that book too. One thing’s for certain. Unlike the trust he gained with Jeffrey MacDonald, he won’t get interview one with Sarah or with anyone who’s truly her friend.