I don’t actually know if that is true or not. I know that more technology exists to determine between isolated homicides, and true serial killer classification. Though that classification has always bothered me as well. If a “Gangster Thug” has killed 30 other rival “Gangsters” over a 20 year period.. Are they technically “Serial Killers”? Under that classification the 570 homicides that took place in Chicago in 2018 were likely due in great part to a few small groups of “Serial Killers”.
I read an FBI "report" a number of years ago, that said they suspected there were serial killers they would never catch - because the killer didn't use a set MO.
I heard or read years ago that at any given time, there are atleast 30 active serial killers in the u.s. .