The President's Lawyer by Lawrence Robbins
Jack Cutler is the golden boy who became president. Rob Jacobsen is a friend of his from high school who became a successful lawyer. After Jack leaves the White House, the body of his mistress, Amanda, is found in Rock Creek Park. All the evidence points to Jack--who insists that Rob has to be his defense lawyer even though Rob himself had been madly in love with Amanda (who dumped him for Jack). Jack insists he didn't kill Amanda and Rob is desperately trying to come up with another theory of who might have done it. There are a couple of surprise twists near the end that the author had subtly hinted at throughout the book. It's an interesting character study. Jack comes off as an entitled jerk most of the time. And despite his success in the courtroom, Rob comes off as kind of weak and a doormat, especially where Jack is concerned. Interesting courtroom thriller.