You might want to take a look at Lonnie Athens (
Wiki - brief and incomplete outline of his theory of violence) - focused first on his research of violent criminals in American prisons. His general conclusion is that, to understand violence, experience is a more important factor than logic, ideology or genetics.
Athens' theory has been considered by Richard Rhodes - generally in
Why They Kill: The Discoveries of a Maverick Criminologist (a brief review of Rhodes' book - but explaining Athens' four stages in a nutshell); and specifically with respect to the SS Einsatzgruppen (in one chapter of
Masters of Death).
In both books, Rhodes concludes:
That is a valid comment re: genocides, serial killers, multiple killers and the "mind of the murderer" in general. As to genocides and Athens' theory, see
Dimensions of Genocide: The Circumplex Model Meets Violentization Theory, by Mark A. Winton (2008, case study of Rwanda).
The bottom line is that Athens' theory generally holds up (although as Winton points out, it is non-exclusive and ties in with other approaches - including some of Grossman[*]) with respect to "bad guys".
However, if it is truly a "general theory", it should also hold up for "good guys" - with adjustments in terminology. Athens gets into that in
Violent Encounters: Violent Engagements, Skirmishes, and Tiffs (Journal of Contemporary Ethnography, 2005), in his Conclusion:
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[*] I've read both of Grossman's books (On Combat and On Killing) - many parts of them more than once, since they obviously relate to actions that are in some cases "war crimes" and in other cases not. I believe Athens' theory is consistent with much of Gerossman's factual material - and also ties in with current training theories and practices for military and police.
Regards
Mike
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