While there is no particular or distinct characteristic of a terrorist, history reveals there are some behaviors that they seem to have in common. Recognizing those behaviors and taking them seriously can alert significant others to pay attention, and to intervene before it is too late. There is a sphere of influence that family and bystanders have that, if enacted, can make a difference and possibly even prevent or change the deadly outcome of a terrorist attack.
What we know, is that terrorists often have a sense of being disenfranchised. Hence, they bond with an ideology-driven group, which gives them a feeling of belonging. This experience is not unlike that of joining a gang.
As a terrorist or gang member, one's personal identity becomes wrapped up in group identification. It is within this cocoon that the terrorist becomes immersed in a cohesive view of life that is seen through the lens of the group. Here, he feels a part of something heroic and bigger than himself.
Because terrorists often demonstrate low self-esteem, narcissism, and a weak center or core, they are particularly vulnerable to the inflated feelings of significance, bordering on omnipotence and immortality. Their cause develops a mythic texture and they project themselves into that theme as a heroic figure. Further, they experience a constellation of grievances, including alienation, perceived injustices and humiliations, for which revenge becomes the antidote. Nothing happens in a vacuum. Though not at first -- as it takes time to be indoctrinated and to accept the option of killing another human being -- eventually, the terrorist transitions to that end through group dynamics.
Thus, the group has the capacity to both mold and design the terrorist, influencing his emerging personality. This communal relationship greatly impacts the terrorist, who may reject anything or anyone outside of this ideological family.
As a result, the terrorist begins to isolate himself from anyone who disagrees with his growing philosophy, though it is this very group that influences his feelings. All along, the personality of the terrorist is developing and changing from the group experience.
If, at this point, someone intervened -- a parent, friend, teacher, or person of influence -- and acknowledged the individual's feelings of isolation and disenfranchisement, challenged his thought process, or separated him from the group, they would have a chance to make a difference and potentially prevent an atrocity.