Communication of Intent to Do Harm Preceding Mass Public Shootings in the United States, 1966 to 2019

Quantifying the risk of mass shootings at specific locations

Mass shootings are horrific events that annually take scores of innocent lives in the United States. Federal, state, and local governments as well as educational, religious, and private-sector organizations propose and enact polices and strategies to protect people from and during active shooter situations. A probabilistic risk assessment of a mass shooting for a specific organization, jurisdiction, or location can be the first step toward evaluating the effectiveness of risk mitigation strategies and determining which strategies might be most appropriate for a location. This article proposes a novel hierarchical method to assess the probability of a mass shooting at specific locations based on available historical data. First, the method generates a probability distribution over the annual number of mass shootings in the United States. Second, the article uses this national number of mass shootings to determine the risk for each state. Third, the state risk assessment is decomposed to calculate the probability of a mass shooting in a specific location such as a school. Multiple ways to assess the risk are presented, leading to slightly different probability assessments for a location. Results indicate that annual probability of a mass shooting in the largest high school in California is on the order of10 - 6 - 10 - 5 $10^{-6}-10^{-5}$ , and the annual probability of a mass shooting in the largest high school in Iowa is about half as likely as in the California school.

A systematic review of literature on homicide followed by suicide and mental state of perpetrators

BACKGROUND

Homicide followed by suicide is rare, devastating and perpetrated worldwide. It is commonly assumed that the perpetrator had a mental disorder, raising concomitant questions about prevention. Though events have been reported, there has been no previous systematic review of the mental health of perpetrators.

AIMS

Our aims were twofold. First, to identify whether there are recognisable subgroups of homicide-suicides in published literature and, secondly, to investigate the relationship between perpetrator mental state and aspects of the incident.

METHODS

We conducted a systematic review of published literature on studies of homicide followed within 24 h by suicide or serious suicide attempt that included measures of perpetrator mental state.

RESULTS

Sixty studies were identified, most from North America or Europe. Methodologically, studies were too heterogeneous for meta-analysis. They fell into three main groups: family, mass shooter, and terrorist with an additional small mixed group. There was evidence of mental illness in a minority of perpetrators; its absence in the remainder was only partially evidenced. There was no clear association between any specific mental illness and homicide-suicide type, although depression was most cited. Social role disjunction, motive, substance misuse and relevant risk or threat behaviours were themes identified across all groups. Pre-established ideology was relevant in the mass shooter and terrorism groups. Prior trauma history was notable in the terrorist group.

CONCLUSION

Research data were necessarily collected post-incident and in most cases without a standardised approach, so findings must be interpreted cautiously. Nevertheless, they suggest at least some preventive role for mental health professionals. Those presenting to services with depression, suicidal ideation, relationship difficulties and actual, or perceived, changes in social position or role would merit detailed, supportive assessment over time.

Comparison of rampage and non-rampage mass shootings in the U.S.: A 5-year demographic analysis

BACKGROUND

Rampage mass shootings (RMS) are a subset of mass shootings occurring in public involving random victims. Due to rarity, RMS are not well-characterized. We aimed to compare RMS and NRMS. We hypothesized that RMS and NRMS would be significantly different with respect to time/season, location, demographics, victim number/fatality rate, victims being law enforcement, and firearm characteristics.

STUDY DESIGN

Mass shootings (4 or more victims shot at a single event) from 2014-2018 were identified in the Gun Violence Archive (GVA). Data were collected from the public domain (e.g. news). Crude comparisons between NRMS and RMS were performed using Chi-squared or Fisher's exact tests. Parametric models of victim and perpetrator characteristics were conducted at the event level using negative binomial regression and logistic regression.

RESULTS

There were 46 RMS and 1626 NRMS. RMS occurred most in businesses (43.5%), whereas NRMS occurred most in streets (41.1%), homes (28.6%), and bars (17.9%). RMS were more likely to occur between 6AM-6PM (OR=9.0 (4.8-16.8)). RMS had more victims per incident (23.6 vs. 4.9, RR: 4.8 (4.3,5.4)). Casualties of RMS were more likely to die (29.7% vs. 19.9%, OR: 1.7 (1.5,2.0)). RMS were more likely to have at least one police casualty (30.4% versus 1.8%, OR: 24.1 (11.6,49.9)) or police death (10.9% versus 0.6%, OR: 19.7 (6.4,60.3)). RMS had significantly greater odds that casualties were adult (OR: 1.3 (1.0,1.6)) and female (OR: 1.7 (1.4,2.1)). Deaths in RMS were more likely to be female (OR: 2.0 (1.5,2.5)) and White (OR: 8.6 (6.2,12.0) and less likely to be children (OR: 0.4 (0.2,0.8)). Perpetrators of RMS were more likely to die by suicide (34.8%), be killed by police (28.3%), or be arrested at the scene (26.1%), while more than half of perpetrators from NRMS escaped without death or apprehension (55.8%). Parametric models of perpetrator demographics indicated significant increases in the odds that a RMS shooter was White (OR: 13.9 (7.3,26.6)) or Asian (OR: 16.9 (3.7,78.4)). There was no significant difference in weapon type used (p=0.35).

CONCLUSION

The demographics, temporality, and location differ between RMS and NRMS, suggesting that they are dissimilar and require different preventive approaches.

Extreme risk protection orders in response to threats of multiple victim/mass shooting in six U.S. states: A descriptive study

Extreme risk protection orders (ERPOs), also known as red flag laws, are a potential tool to prevent firearm violence, including mass shootings, but little is currently known about the extent of their use in cases of mass shooting threats or about the threats themselves. We collected and abstracted information from ERPO cases from six states (California, Colorado, Connecticut, Florida, Maryland, and Washington). Ten percent (N = 662) of all ERPO cases (N = 6787) were in response to a threat of killing at least 3 people. Using these cases, we created a typology of multiple victim/mass shooting threats, the most common of which was the maximum casualty threat. The most common target for a multiple victim/mass shooting threat was a K-12 school, followed by businesses, then intimate partners and their children and families. Judges granted 93% of petitions that involved these threats at the temporary ERPO stage and, of those cases in which a final hearing was held, judges granted 84% of final ERPOs. While we cannot know how many of the 662 ERPO cases precipitated by a threat would have resulted in a multiple victim/mass shooting event had ERPO laws not been used to prohibit the purchase and possession of firearms, the study provides evidence at least that ERPOs are being used in six states in a substantial number of these kinds of cases that could have ended in tragedy.