First, hat tip to Active Response Training for putting this on their weekend knowledge dump.

Secret Service’s National Threat Assessment Center recently put out a report “Mass Attacks in Public Spaces: 2016-2020. You can go to the link and get your own copy.

The definition of a mass attack used by the report is an incident in which three or more people, not including the perpetrator, were harmed during an attack in a public or semi-public space. Between 2016 and 2020, the NTAC identified 173 of these incidents.

The TLDR is that the perpetrators were known to have issues that made people wary of them, often had a history of violence, and most used guns that were often possessed illegally. This is my shocked face after seeing the results of investigations into some of the more high profile cases.

From the Executive Summary:

The 173 attacks contained in this report impacted a variety of locations, including businesses/workplaces, schools, houses
of worship, military bases, nonprofit service providers, residential complexes, public transportation, and open spaces.
In many cases, the attacker had a known affiliation with the site of the attack.

Snip

• Most of the attackers had exhibited behavior that elicited concern in family members, friends, neighbors, classmates,
  co-workers, and others, and in many cases, those individuals feared for the safety of themselves or others.
• Many attackers had a history of physically aggressive or intimidating behaviors, evidenced by prior violent criminal
  arrests/charges, domestic violence, or other acts of violence toward others.
• Half of the attackers were motivated by grievances, and were retaliating for perceived wrongs related to personal,
  domestic, or workplace issues.
• Most of the attackers used firearms, and many of those firearms were possessed illegally at the time of the attack
• One-quarter of the attackers subscribed to a belief system involving conspiracies or hateful ideologies, including anti-government, anti-Semitic, and misogynistic views.
• Many attackers experienced stressful events across various life domains, including family/romantic relationships, personal issues, employment, and legal issues. In some of these cases, attackers experienced a specific triggering event prior to perpetrating the attack.
• Over half of the attackers experienced mental health symptoms prior to or at the time of their attacks, including depression, psychotic symptoms, and suicidal thoughts

Again, this is not surprising to those who have seen coverage of these types of attacks over the years.

Looking in the back, the NTAC had some interesting stats. Approximately 73% of the attacks were done with a gun. Of those, three-quarters were done with handguns. Here’s another part I found interesting:

Mass shootings have been perpetrated by those who were legally prohibited from possessing firearms. One-third of attackers in this study were prohibited by federal law from purchasing or possessing a firearm, including those with a prior felony or domestic violence conviction, fugitives from justice, those previously adjudicated incompetent or involuntarily committed to a mental health institution, and those who were currently the subject of a domestic-related protection order. Despite these prohibitions, 38 of these attackers used firearms during their attacks, including those that were acquired through straw purchases, theft, purchases from private sellers, and purchasing parts online.

emphasis mine

IMHO, those of us in the gun community already know some of this. We also have the benefit of being able to discern what would be considered normal behavior for a gun enthusiast and someone who’s acting in ways that could be indicators.