POP Center Responses Gunshot Detection Page 4
Responding to Gunshots
Gunshot Incidents
Once an AGDS is in place, officers and detectives will have to actively respond to and investigate the incidents. At present, there is little research-based guidance on what constitutes best practices, so most recommendations are based on practitioner experience.
Information
A good response begins with useful information. Dispatchers should receive training in determining the number of gunshots and whether multiple shooters are involved. If the gunshot detection information is limited to what is relayed to the field by dispatchers, it should include the following critical details:
• An accurate location description. An address by itself is useful only if the incident occurred on a residential street. If it occurred in a backyard or a park, officers should be made aware of this fact, especially if the responders do not have access to a map with exact locations.
• Information on the exact number of gunshots detected. Knowing about how many shots were fired allows officers to dedicate the appropriate amount of resources to finding evidence.51
If patrol officers have direct access to the acoustic data, the responding officer should:
• Respond to the mapped location of the detected gunfire to determine where to look for evidence
• Listen to the gunfire while responding or inspect the wave pattern if it is safe to do so (doing so requires a two-officer response). By doing so, they can gather crucial information about the number of rounds and the number of guns involved in the incident.
Response Time
Ideally, police will respond at highest priority to AGDS alerts. A fast response increases the chances of finding victims and witnesses and providing life-saving actions. Responding quickly to gunfire alerts, however, may not always be possible. Some agencies may not have the resources to assign the highest priority response to AGDS alerts, especially if they deal with high-volume gun incidents and frequent AGDS alerts. When compared to citizen gunshot reports, AGDS alerts do not lead officers to a higher percentage of assaults or homicides.52 An emergency police response also may increase the risk for accidents and elevate responding officers’ stress.† Clearly, AGDS responses may induce such stress, and more research is needed to examine whether such calls create unnecessarily dangerous conditions for citizens and officers.
† In an experimental study of an active shooter incident, for example, roughly 20 percent of participants recalled seeing a firearm in the hands of the mock offender, even though the gun remained in the person’s waistband (Hope et al., 2015).
If highest priority responses are not feasible for all AGDS alerts, agencies may consider developing a system for acoustic alerts that distinguishes between alerts that are likely tied to in-progress gun violence and those that are not. Alerts may not all be equal in their level of severity. In St. Louis, for example, alerts with more than seven rounds fired account for half of assaults and homicides, so the number of rounds fired may provide some justification for determining the urgency of the police response.53 The occurrence of a 911 call for gunfire in addition to the AGDS alert may provide another indicator of seriousness. More research is needed to understand which types of alerts have a higher probability of indicating shootings that involve victims.
Most cases in which a victim is shot are called in by residents, but AGDS may improve the police response time and evidence recovery. Nonetheless, that improvement should be put in perspective. In Cincinnati, which has a relatively low number of gunfire cases (which receive high-priority police response), the average response time for gunfire alerts is between 4 and 5 minutes after receiving the notification (so a total of 5–6 minutes post-gunfire, accounting for incident review).54 It is doubtful that many shooters and victims hang around for long after the firing of a gun, which may explain why the difference between citizen calls and AGDS alert response times is not likely to significantly affect arrest probabilities.55 However, the geographic precision of AGDS could make a critical difference in successfully collecting evidence and locating victims in need of assistance.
Investigation
Thoroughly investigating gunfire incidents is arguably even more important than providing fast response times, both for solving and preventing the incidents. Collecting ballistic evidence and locating victims, offenders and witnesses are, of course, primary objectives. Consistently responding to and investigating AGDS alerts, and interacting with the public during these calls, can be deemed a form of hotspot policing,56,‡ but without more purposeful preventive action, it is unlikely to effectively reduce shootings at that location. Within the situational crime prevention framework, AGDS may help “increase the risk” of shooters being identified and punished.§ Responding officers should talk with residents and the business community about the shooting incidents to identify the underlying conditions that might be contributing to them. Officers should understand the difference between conducting a criminal investigation of the incident (i.e., who fired this shot?) and an analysis of the problem (i.e., why are shots being fired at this location?). In Cincinnati, the difference in responses might explain why the city experienced substantial crime reductions after implementing AGDS but other sites have not.57
‡ See Problem-Solving Tools Series, No 14. Understanding and Responding to Crime and Disorder Hot Spots, for further information
§ See the Twenty-Five Techniques of Situational Prevention at https://popcenter.asu.edu/content/25-techniques.
Locating shell casings or projectiles during the initial response is often difficult because shootings often occur at night. Good practice is therefore to return to the scene when visibility improves. Finding casings can be especially difficult because they may roll into pavement cracks, grass, or weeds or under vehicles (see Figure 4).
Figure 4. Shell Casing in Alley, Hidden Among Debris and Weeds
Source: Photo by author.
Keeping track of the casings and the scene they belong to can be complicated as well. For example, many gunfire locations experience repeated incidents over time, meaning that casings could be from a prior incident. Given that this work can be time-consuming, good practice is to assign specific personnel to follow-up investigations and establish clear protocols for evidence collection and case attribution.
Link analysis and National Integrated Ballistic Information Network (NIBIN) identification are critical tools that allow agencies to connect guns to prior offenses and gunfire incidents.58 Link analysis creates connections between bullets or casings that may have been used in prior shooting incidents. Forensic specialists can then examine the unique markings, specific to one firearm, from bullets and casings and link them using specialized software tools. In addition, retrieving fingerprints from some casings may be possible. Ballistic evidence gathered during responses to acoustic alerts can supplement NIBIN link analysis and enhance investigations in Crime Gun Intelligence Centers (CGIC).59 Quick identification and linking of casings can improve case resolution, but the sheer volume of casings that acoustic systems can deliver can also be beneficial.60 Indeed, though many casings discovered by acoustic alerts may not be from shootings with victims, preserving the records may help detectives investigate future assaults by providing locations where the gun was fired prior to the incident. Link analysis of casings can also assist in uncovering offender networks and provide insights into the life cycle of firearms.
Officers and detectives who investigate assaults and homicides should be trained in the use of acoustic data.61 Some vendors provide training for their applications, but more involved training may be needed if raw data have to be manually extracted and mapped. Vendor data portals, for example, generate a wealth of gunfire data for an agency. In addition to gunfire detections forwarded to dispatch or officers in the field, sensor activations also include gunfire incidents outside the coverage area (which might be less geographically accurate) and even “non gunfire” incidents, some of which may have been falsely dismissed.62 Such data can assist active investigations by allowing investigators to:
• Investigate incident locations to determine whether other recent gun-crime incidents occurred at the same site, which may be important if the casings retrieved do not match the firearms used in the incident and may also establish whether prior conflicts have occurred in the area.
• Verify victim, offender, or witness statements. Gunfire data from acoustic systems can be used to verify information and statements given during an investigation. Verification may be particularly important when victims are first contacted in a hospital and if the crime scene is either unknown or contaminated. Gunshot victims are not always cooperative and verifying the veracity of their statements is important to quickly establish the accuracy of gunfire locations and save investigative time in the field.
Case Study: Evaluation of Phoenix Crime Gun Intelligence Center 63
In 2017, the Phoenix Police Department received funding to establish the Phoenix Crime Gun Intelligence Center (CGIC) and pilot a novel, cost-effective mobile gunshot detection system without incident review. Establishment of the CGIC was associated with enhanced ballistic processing and improved clearance rates, although prosecutorial outcomes were not affected. The study reveals the importance of CGICs in general, but here we focus on the pilot of the gunshot detection systems, which also proved worthwhile. Acoustic sensors were placed in the areas with the most reported shots-fired calls for service; two control sites were also assigned. After deployment of the system, only 12 percent of total gunfire alerts came from residents, indicating that gunfire had previously been substantially underreported. Prior to implementation, only 8.6 percent of gunfire incidents led to shell casings being detected, but during the experiment, that percentage increased to 25.2. Firearm recoveries and arrests also increased, but these results were not statistically meaningful. Response time to gunshot incidents decreased, but these results were not statistically significant given the small number of cases. Although these results must be seen as preliminary given the limited scope of the system implemented, they do suggest positive investigative outcomes.
Gunshot Problems
Preventative or problem-solving efforts may benefit from AGDS data. Most agencies use acoustic systems reactively––responding to incidents as they happen––but not to inform broader prevention efforts. Because gunfire problems tend to be highly concentrated in place and time (not widely diffused across a jurisdiction) and because AGDS does detect most gunfire,64 AGDS data can help police detect the concentrated locations and times.
Compared to traditional gun-violence data, AGDS alert data provide greater numerical frequency, which can help to more rapidly identify specific properties or locations that present an ongoing gunfire problem. In addition, because much gun violence is retaliatory and victims are often uncooperative, 65 analysis of gunfire data can help identify emerging conflicts, particularly if casings are analyzed and traced to specific guns and their known owners.66,†,‡ Figure 5 is an image of gunfire hotspots showing 26 alerts and 76 rounds over a 3-month period near a specific (vacant) property (the street names were obscured by the author). Each yellow balloon notes a separate alert and the number of rounds fired.
† See Problem-Specific Guide No. 74, Retaliatory Violent Disputes, for further information.
‡ One way to identify gunfire hotspots with acoustic data is by using the “optimized hotspot” function in ArcGIS. By using the option to create weighted points and selecting an appropriate distance band, a user can identify highly localized gunfire hotspots. In essence, the software will let a user select a threshold for the minimum of gunfire alerts to occur within a predefined area, returning the average spatial location. The quality of the results, of course, depends on the amount of data fed into the function.
Figure 5. Image of Gunfire Hotspots
Source: Screenshot from ShotSpotter’s Insight Portal.
Finding gunfire hotspots is the easy part; developing strategies that can successfully curb gunfire is harder. No studies currently offer concrete evidence-based practices specifically for using gunfire data to reduce gunfire.67 Although hotspot patrols are a reasonable option for achieving at least short-term gun violence reductions, they are difficult to sustain and may strain or damage community relations. A careful problem-solving approach will likely be more effective if it can address some of the place-based opportunities that prompted the gunfire to concentrate. For example, vacant lots and overgrown alleys can provide cover for illegal gunfire. Greening, renovating, and tearing down vacant homes can reduce crime.68,§ Identifying gunfire hotspots would be a good start to such efforts. Similarly, if police can identify individual problem properties, they can work with other agencies to improve management of the property.¶ Code enforcement, nuisance abatement, social services, and violence interrupters can also contribute to interventions at such locations, although whether such strategies are effective is currently unclear. As a stopgap, police can deploy additional technologies such as mobile surveillance trailers in gunfire hotspots. Initial results from St. Louis indicate that such units can strongly deter gunfire.69 Naturally, the results of high-visibility technology may last only as long as the technology is deployed, and longer-term solutions may be required. Another option is to implement consent-to-search programs, which would allow police to seek residents’ consent to search their homes for firearms in locations where gunfire levels are high.70 Finally, many departments engage in public awareness campaigns to reduce celebratory gunfire.71 Unfortunately, little is known about the efficacy of such programs. In short, at least seven responses to gunfire hotspots are potentially effective:
(1) Targeted preventive patrols
(2) Physical modification of the environment
(3) Property management improvement
(4) Targeted conflict resolution with violent retaliatory disputants
(5) High-visibility camera technology to deter offenders
(6) Targeted consensual searches of homes for firearms
(7) Crime prevention publicity campaigns (e.g., to discourage celebratory shooting on holidays).†
§ See Problem-Specific Guide No. 64, Abandoned Buildings and Lots, for further information.
¶ See Response Guide No. 11, Using Civil Actions Against Property to Control Crime Problems, for further information.
† See Response Guide No. 5, Crime Prevention Publicity Campaigns, for further information.
