Via the Public Library of Science, Daniel Lende on the need to understand horrific mass shooting as a cultural practice with underlying meaning, rather than as anomalous, randomized insanity:

Paul Mullen, the esteemed Australian forensic psychologist, invokes cultural scripts as central to understanding why young men like James Holmes, Anders Breivik, and Jared Loughnerdo what they do. It is not because they are insane, some idea that seized them from the inside. Rather, they act out something – and the young men who do so are not random members of society, but have definable characteristics.

Mullen compares these mass killings to the Malaysian amok, a recognized “culture-bound syndrome” often defined as a “spree of killing and destruction (as in the expression “run amok”) followed by amnesia or fatigue.” (For more references, [search] Google Scholar for “amok Malaysia”.

Mullen also counters the common explanation in the United States and elsewhere that these killers must somehow be insane or mad. He distinguishes between a common sense view of mental health – “of course he was mad” – and a technical sense of mental health (“clinically insane”). Most of these men are not clinically insane in the way typically recognized.

Interestingly, they’re not like many offenders, they don’t tend to have problems with alcohol and drugs. They’re certainly not impulsive, quite the reverse. These are rather rigid, obsessional individuals who plan everything extremely carefully. And most of these massacres have been planned for days, weeks, sometimes months ahead.

Likewise there is a religious connection too in some cases. The New York Firefighter shooter it turns out was a Satanic...

Death to the infidels, PRAISE SATAN...

There is no cultural or religious connection to it.

Take a rat, put it in a cage, keep adding more rats, eventually you'll get to a point where the rats start killing each other for no apparent
reason.