The Bone Tree (Penn Cage #5) by Greg Iles

Southern prosecutor Penn Cage is caught in the darkest maelstrom of his life. The heartbreaking but seemingly straightforward death of his father's African-American nurse, Viola Turner, has fractured Penn's family and turned Dr. Tom Cage into a fugitive from justice. And in the search for his father and his reasons for running, Penn has unwittingly started a war with a violent offshoot of the KKK, the Double Eagles, whose members seem to know much more about Tom's past than Penn or his mother ever did.