This study examines the factors that differentiate solved and unsolved homicides in Australia. Based on data from the National Homicide Monitoring Program and questionnaires completed by police homicide investigators, the study analyses factors associated with the homicide incident and factors associated with the victim. The study finds that unsolved homicides are more likely than solved homicides to occur in the course of other crime and at a location other than a residential premise. The victims of unsolved homicides are more likely to be killed with a firearam, and are likely to be aged 30 years or older. The homicide investigators' responses also highlight the availability of sufficient resources, crime scene factors and witness factors as major themes in clearing up homicides, and identify major impediments to solvability.