The Night is Watching by Heather Graham
The Krewe of Hunters is a unit of the FBI that uses paranormal means to investigate unusual crimes. In Lily, Arizona, a 100-year-old skull has been found and it is up to Jane Everett, forensic artist for the Krewe, to identify her. Working with Sheriff Sloan Trent, Jane uncovers a mystery from the past with ties to a current string of murders.
The Night is Watching is the ninth in the series by Heather Graham. If you are looking for a paranormal romance, that is also a historical mystery, this is a series you should try. The main investigators, in this case, Jane and Sloan, solve the crime with ghostly assistance and historical research. Along the way, they also find love.