In San Bernardino, focus on the murderous partnership.

James Alan Fox 6:56 p.m. EST
December 3, 2015

Most mass killers are enabled by social isolation, only rarely do pairs bring out the worst in each other.

At least 14 killed and 21 injured in a mass shooting at an office building in San Bernardino, Calif., allegedly by a couple armed and dressed for battle. The extent of carnage is absolutely shocking, while the relationship of the suspected gunman and gunwoman is surprising, but only somewhat so.
It is quite true that the vast majority of mass killings involving firearms are perpetrated by lone assailants. Of the more than 200 cases in the USA

The prototypical lone gunman bent on revenge usually reflects an angry, dispirited or sometimes deranged individual who seeks revenge against those whom he sees as his tormentors. The perceived enemy are those people who caused life to be so unlivable. They would have to pay for making everyday existence a living hell. Occasionally, in the purely random massacres, the target is not some specific workplace, but society in general, seen as a corrupt world in which all the breaks go to other undeserving people.

The lone shooter is enabled by his social isolation. He has no real support system to help him deal with life's frustrations and disappointments and, more important, no one to provide a needed reality check on his unrealistic view of his victimhood. The lack of others allows the loner to see the world through a distorted lens.

When couples kill be it a married couple (as appears to be the case in the latest bloodbath), brothers (as in the Boston Marathon bombing), pseudo father and son (as in the DC sniper murders), the presence of a close confidant, rather than the absence, is enabling, so long as the other participant is of like-minded perspective.

In these deadly duos, the association is emboldening and reinforcing. It is far easier to kill when someone else shares the responsibility and, more critically, reinforces the idea that it is the right thing to do. It becomes a case of "us against the world' thinking.

The key to understanding the motivation of partners in crime both those that depend on familial connections and others such as the Columbine massacre that involve friends is to focus more on the partnership than on the crime. It is at last arguable that the attack would not have occurred without the partnership bond. Typically, one person is the leader who thrives on having a willing foot soldier, while the other seeks approval from his or her mentor. Each brings out the worst in the other, and together they see the virtue in some deadly plan.

As compared with lone gunmen, mass killer partnerships and teams are especially dangerous. Of course, two heads are almost always better than one in terms of planning a strategy of attack and making the necessary preparations. Plus, once at the targeted location, two shooters can wreak double the havoc in terms of body count.

But the dangerousness of gangs of two or more lies also in the power of group think. While there is the possibility of a successful intervention to derail the deadly designs of the lone wolf, team killers feed off each other to find inspiration and resolve. They can easily insulate themselves from others, especially when motivated by some political ideology.

Finally, a single would-be killer can abandon his fantasies of violence without having to appear weak. However, when co-conspirators are involved, there is pressure to follow through, to stay loyal to the cause, and not let your accomplices down.

It is said that "everybody needs somebody sometimes," but sometimes that somebody is only there to facilitate an extreme act of violence.

James Alan Fox is the Lipman Professor of Criminology, Law and Public Policy at Northeastern University and a member of the USA TODAY Board of Contributors. He is co-author of Extreme Killing: Understanding Serial and Mass Murder.