Mitigation Actions

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We identified three effective actions to mitigate casualties: (1) putting distance between shooters and potential victims, (2) using movement, and (3) forming barriers to separate shooters from crowds. The goal is to keep shooters from surprising people at close range and when opportunities to escape are restricted.


Distance provides more space between where shooters enter a site (or rooms within a site) and bystanders. Implementation of distance could include making longer walk-ups or entry areas (vestibules, etc.), which permit onsite personnel to see an attacker, sound the alarm, and prepare subsequent security measures.

Distance can and should include having security personnel engage people who they do not know, especially if those people are acting suspiciously. (Note our finding that plotters frequently engage in pre-attack site surveillance and probing.)


The following tips were relayed to us by our expert panelists. They were developed for ushers and guards at houses of worship but can be applied much more widely.

Welcome parishioners and congregants.

If you do not know someone, introduce yourself and ask them their name.

If someone is visiting, ask a simple question: for example, "Where are you visiting from?"

Ask whether the person is requesting any special considerations; for instance, "Are you saying a prayer for someone who is sick or commemorating someone's death?"

Notice whether the person fails to make eye contact and if they are dressed appropriately for the venue and weather.

Take note of whether they appear to be concealing something, walking awkwardly, or adjusting their waistband.

Trust your instincts.


Movement increases the ability of bystanders to move around and escape, such as by providing more exits. Moving targets are much harder to hit, and the more quickly bystanders can escape the line of fire, the lower the number of casualties will be.


Barriers physically separate shooters from crowds. The implementation of barriers may include locked doors; controlled entry areas, such as lobbies or reception areas before crowded spaces; and additional walls or other physical barriers. The goal is to prevent shooters from clearly seeing and engaging bystanders.

The importance of locks and other barriers is shown by one recent study, which found that, as of 2017, no active shooter had successfully breached a locked door in the United States (Martaindale, Sandel, and Blair, 2017).

These three mitigation actions can be implemented together, with such distance measures as longer walk-ups and vestibules providing the time needed to lock doors into crowded areas.

Beyond implementing security measures, large private-sector entertainment venues have embraced developing response playbooks and conducting regular tabletop exercises with all partner agencies, including law enforcement. These efforts consider different plan components to address what responses would look like at different locations in a given venue.

Notes on the Effective Actions

In this section, we provide more information on where these actions come from.

We developed these three mitigation actions by comparing descriptions of a sample of failed and zero-fatality mass attacks with descriptions of high-casualty attacks and identifying the differing factors to determine why some attacks ended without casualties. We found three broad categories of factors:

  • factors describing site characteristics that contributed to ending the attacks early; these factors can be summarized as those that put distance, movement, and/or physical barriers between would-be shooters and bystanders, as described above
  • factors describing actions by on-scene security (including off-duty officers) and bystanders to end the attack (which we address below)
  • factors describing actions by shooters that ended the attack, including both intentional actions (e.g., deciding to stop) and unintentional actions (e.g., the gun jammed).

Special Note on Shooter Characteristics

Some key factors associated with casualties had to do with the shooter, both in our analysis and in the literature (e.g., Blair, Sandel, and Martaindale, 2020; Lankford and Silver, 2020). Shootings in which the perpetrator had more skill in using firearms and/or brought more firearms with more ammunition were, unsurprisingly, associated with higher casualties. Higher casualties resulted from both the shooter's capability and fewer interruptions because of gun jams or other mishandling problems. The connection between a shooter's preparedness and high casualties reinforces the need to report and follow up on warnings related to individuals who are seeking to learn to kill large numbers of people with firearms and/or who are attempting to amass arsenals to do so, as discussed in the Prevention section of this toolkit. (These reports are for training and weapons acquisition without a benign explanation, such as hunting.)

Next Page in the Mitigate Phase

Tools and Resources for Securing Venues