Mission
The NCIS mission is to investigate and defeat criminal, foreign, and terrorist intelligence threats to the United States Navy and Marine Corps, wherever they operate: ashore, afloat, or in cyberspace.
General Criminal Investigations 

NCIS investigates a broad range of crimes against persons and crimes against property, including such serious crimes as assault, sexual assault, robbery, kidnapping, and homicide.  NCIS investigates all deaths of naval personnel that occur in non-combat, non-medically attended circumstances, in order to determine whether criminal causality played any role. Other crimes subject to NCIS investigation include crimes against property and such offenses as false statements, obstruction of justice, and perjury.
 
This is an official Department of Navy website.
Naval Criminal Investigative Service, 27130 Telegraph Road, Quantico, VA 22134