All I have heard is that after CG disappeared from the same area as SS and JR, that police started believing that they were dealing with a serial killer. Which the CSK case is a good example of a definition of a serial killer.
A serial killer is a person who murders three or more people,[SUP][1][/SUP] usually in service of abnormal psychological gratification, with the murders taking place over more than a month and including a significant break (a "cooling off period") between them.[SUP][1][/SUP][SUP][2][/SUP] Different authorities apply different criteria when designating serial killers;[SUP][3][/SUP] while most set a threshold of three murders,[SUP][1][/SUP] others extend it to four or lessen it to two.[SUP][3][/SUP] The Federal Bureau of Investigation (FBI), for example, defines serial killing as "a series of two or more murders, committed as separate events, usually, but not always, by one offender acting alone".[SUP][2][/SUP][SUP][4]
-Wikipedia[/SUP]
The FBI also has a quick meme for dealing with killings.
One killing is random, 2 is coincidence, three is a Serial and also a pattern.