These crimes are extremely difficult to solve because the murderers typically leave little evidence at the crime scenes, rarely have any prior connection to their victims, and do not have an obvious motive to kill. In addition, serial and mass murderers often stake out their victims for weeks to ensure there will be no witnesses. As a result, serial and mass murderers tend to evade detection longer than most other killers. Therefore, law enforcement agents encounter many challenges when trying to identify and apprehend serial and mass murderers. Criminal profilers, however, can help law enforcement agents address some of these challenges by providing physical, psychological, and even background profiles of serial murderers.
Read Serial Murder: Pathways for Investigation.
http://www.fbi.gov/news/stories/2014/october/seria…Review FBI Law Enforcement Bulletin “Criminal Investigative Failures: Avoiding the Pitfalls (Part Two)”
http://www.au.af.mil/au/awc/awcgate/fbi/investigat…Read Kocsis, R. N.