Understanding the motivations of mass shooters is key to successful law enforcement strategies

The study - "Mass Shooters in the USA, 1966-2010: Differences Between Attackers Who Live and Die" by Adam Lankford, published in the June 2013 issue of the academic journal Justice Quarterly -- is the first largescale academic analysis of "active shooters," defined by the US Department of Homeland Security as: "an individual actively engaged in killing or attempting to kill people in a confined and populated area."

Approximately 38% of mass shooters commit suicide by their own hand, and up to 10% successfully orchestrate "suicide by cop." In addition, it is thought that a significant percentage of attackers who survive are also clinically suicidal, but they failed in their attempts to die or changed their minds at the last moment although, as Adam Lankford notes, this is difficult to prove because suicidal intent is so difficult to measure. He writes:

"It may be impossible to know how many mass shooters who died at the hands of law enforcement were intentionally orchestrating 'suicide by cop,' or how many of those who were ultimately arrested had originally intended to perish instead."

Previous research suggests that there are fundamental psychological and behavioral differences between offenders who commit murder and offenders who commit murder-suicide. Lankford's study goes further, because it assesses mass shooters as a coherent offender type, basing its analysis on information from one data-set, rather than several different sources, which enhances the accuracy of the regression analysis technique.

The data source for Lankford's study is a New York City Police Department (NYPD) report of mass shooting incidents worldwide from 1966 to 2010. From this, Lankford excluded all non-USA attacks and all attacks that yielded fewer than two casualties. The remaining 185 incidents were then analysed using chi-square (w2) and ANOVA tests to determine whether or not the average differences between mass shooters who lived or died could be attributed to mere chance.

Lankford's analysis identifies numerous differences that have an impact on whether the perpetrator is taken into custody or dies as a result of the attack. He postulates that two factors may influence the outcome of a mass shooting event: training officers to recognize which mass shooters are most likely to commit suicide by their own hand or attempt "suicide by cop"; and providing officers with detailed information about the attack (such as the offender's number of weapons, number of victims killed, and decision to attack at an open commercial site, factory, or warehouse).

Crucially, Lankford points out that attack resolution outcomes may not be solely determined by offenders' individual psychology -- outcomes may also be the product of situational factors when the event is underway. For instance, it was not possible to assess, from the NYPD data, whether law enforcement behavior is essentially a constant in the determination of whether mass shooters live or die, or actually an explanatory variable itself.

Lankford postulates that, because officer discretion is an inevitable part of policing it is conceivable that some officers would have felt more threatened, angry or vengeful and therefore may react differently when responding to some mass shooting incidents than others.

The article, which includes a detailed review of existing literature on the subject, and an appendix listing all the offenders and attack location types, concludes:

"… law enforcement officers must be careful not to overreact … or allow their actions to become overly predetermined. Ultimately, they should respond to each incident with the level of force dictated by the situation itself."