When my book went to press there were 8,894 unsolved murders in New York since 1985.
Los Angeles, the next largest city in America, had 8,000 going back to 1960.
Fairfax, VA, had 75 going back to 1964.
If you want to try to figure out how many cold cases are in your city, go to the FBI’s website and download the Uniform Crime Reports, aka Crime in the United States. Right now they have reports going back to 1995. You can also go to the library or local college if they offer a criminal justice degree, and find reports going back to 1930.
In each report, you can look up the national clearance rate for murder that year and from that estimate how many murder cases in your city likely went cold. It’s generally around a third.