Information about the personality makeup and motives of mass shooters is usually slow to dribble out. Security and privacy issues make it difficult to learn a great deal about these individuals until a fair amount of time elapses and sometimes not even then.
One thing we do hear in nearly every case is that the shooter was a “loner.” This aspect of his personality is described in various ways—that he is shy, withdrawn, isolated, reclusive, showing symptoms of Asperger’s Disorder, and so forth. We frequently hear that these individuals were marginalized, not accepted by their peers and not well-liked in general.
An understanding of the mental processes of these killers will show that they have “marginalized” themselves. They are secretive individuals who do not want others to know them. They may be highly intelligent, achieve high grades in school, and even obtain responsible positions that draw on their talents. However valued they may be for their accomplishments, they are only superficially sociable, usually not even that.
These people lack empathy and rarely put themselves in the place of others. Determined to prevail in any situation, they are uncompromising. They see themselves as special and look with contempt upon others whom they do not think are as gifted as they.
They are “loners” because they interact only minimally with other people. They see human relationships as avenues for their own buildup and affirmation. They do not believe that they have much to gain by truly getting to know others. Sometimes they show their scorn by bullying others. Usually, they just remain a mystery because they are so disengaged.
Some mass shooters appear to display symptoms of Asperger’s Disorder in that they “lack social or emotional reciprocity” and they manifest a “failure to develop peer relationships appropriate to their age” (see the DSMIV-TR of the American Psychiatric Association). But as information becomes available, what we have seen is that if one must apply a label of a mental disorder, what often (although not always) applies is elements of a “personality disorder,” usually of an antisocial type.
These individuals regard the world as their own personal chess board. They seek to control others, have unrealistic expectations, and pursue single-mindedly what they want with little regard to the impact on other people. They are constantly angry at a world that they believe denies them what they are due. The anger is always present, but often not observable. It is like a cancer that metastasizes. And then, there is the one slight too much, the one perceived insult (sometimes a string of them), and the anger finds a target or multiple targets.
These are not likeable individuals. No one seems to have known them well. They marginalize themselves, rejecting the world well before the world rejects them.
Why they are this way we do not know. We do know a fair amount about the thought processes that result in their being loners.