This is a unique list for moments when mass murderers and other criminals ended up affecting each other's behaviors, or share a relationship or connection with each other. You are allowed to add on to it.
Ex: Eric Harris's comments on the O.J. Simpson trial.
Michael Soles ruining a planned murder by the BTK
Jennifer San Marco's obsession with Son of Sam
Joel Rifkin's encounter with Colin Ferguson
Salman Abedi and Ian Brady being kept in the same mortuary
Mass murderer to Mass murderer doesn't count.
"The average is 5.5? I thought it was 4. This is very unsettling" - Elliot Rodger