There is rarely a trigger that puts a sociopath 'over the edge'. Those of us who live without this disorder live within the boundaries of a moral compass, and experience empathy, sympathy, and logic - sociopaths are devoid of these things and have no boundaries.
In essence they are always 'over the edge', it is only the degree that differs.
The problem with trying to understand or analyze a sociopath, is that we use our rational and emotional brain to do it - understanding how they work requires that we set aside the thoughts of what 'we' would do.
There is no rationale, there is no reason - well not one that you or I will understand, the ONLY person it will make *sense* to is the socipath themselves. Other socipaths won't get it either.
Socipaths are what they are, and we will likely never really understand, for though the illness is diagnosable, it is as individual to each sufferer as epilepsy or diabetes.
It is those who recognised these behaviours and ignored them that we should try to analyse, so that we can attempt to prevent this happening again.