The Last Witness by Joel Goldman

Kansas City trial attorney Lou Mason is back...and this time, it's personal. Hired to defend the accused murderer of Jack Cullan, a local lawyer and political fixer, he finds himself working for his close friend who watches his back, ex-cop Wilson "Blues" Bluestone, Jr. Mason unearths the kind of secrets someone will do anything to keep. And as he closes in on a desperate killer who's leaving a bloody trail through very high places, Mason may be setting himself up as the next target.