Bollinger County Sheriff Darin Shell has confirmed that investigators are looking at several "persons of interest" in connection to last September's shooting death of 35-year-old Jeffrey Scott Robins.  Shell says they are continuing their search for someone they believe walked into Robins' unlocked rural home on County Road 834 the afternoon of Sept. 6 and fired one shot into the back of his head as he slept.  Robins repossessed cars as owner of HJR Towing and Recovery in Marble Hill was going through a divorce at the time of the murder.  The sheriff's office is being assisted by the Missouri State Highway Patrol's Division of Drug and Crime Control, a special unit assigned to investigate homicides and other violent offenses across the state, assisting local agencies where the deaths occur.  Robins' four children, ranging in age from 6 to 16, live with their mother.