Homicide Clearance Rates in Decline - Why?

"Get used to it, I ask WHY a lot." -Professor Kim D

   I have read the first 2 chapters of "Mind Hunter" and it is fascinating.  One of the things that really struck me was the fact that the Homicide Clearance Rate has been in decline since the 1960's.  Incredible, given all the advanced 'scientific and technological tools' available today.  The book cites the changing nature of violent crime as a possible factor.  In the past most violent crime occurred between people who knew one another, but today we see more violence between strangers.  Additionally, these crimes seem to lack logical motives.

   "Mind Hunter" was published in 1995, nearly 20 years ago, so I wanted to see if these stats were still true.  I found this article on the Bureau of Justice Administration https://www.bja.gov/Programs/BJAHomicideProgram.pdf  which states that in 1965 the rate stood at 91%, but since 1990 it has never exceeded 67%.  Below you can see the stats for 2012.  Wow, not exactly good news.  

Photo from the FBI web site:  http://www.fbi.gov/about-us/cjis/ucr/crime-in-the-u.s/2012/crime-in-the-u.s.-2012/offenses-known-to-law-enforcement/clearances

  If you want to read more about why the Clearance Rates have declined, you may want to read this article from the National Institute of Justice; "Clearing Up Homicide Clearance Rates".  https://www.ncjrs.gov/pdffiles1/jr000243b.pdf