With serial killers I also wonder if there's anything to do with the U.S.'s geography/landscape/actual physical arrangement of people? (Any of the studies reference this- do serial killers tend to be more focused in cities, or outside of them?)
I know that is a *component* of gun culture- to get super-simple about it, gun ownership is a different issue in more-rural america (where hunting is a big cultural thing, including identity, pastime, family bonding, etc and guns are inherently part of that) than in more-urban america.