A Man Who Is Serving Life In Prison For Killing A Bristol Tennessee Police Officer Is Claiming Mental Illness. Nikolaus Johnson Is Now Seeking A New Trial In Sullivan County Criminal Court. He Was Convicted In The 2004 Death Of Officer Mark Vance Who Was Answering A Call Of Domestic Violence. A Doctor From NYU Testified Yesterday That Johnson Suffers From Brain Injuries. He’s Just One Of Many Witnesses Expected To Testify During Hearings This Week. Johnson’s Been Trying To Get A New Trial Since 2014.