SEATTLE POLICE DEPARTMENT MEMORANDUM

TO:

Council President Tim Burgess

DATE: 12/4/2015

FROM:

Brian Maxey, Chief Operating Officer

SUBJECT:

ANALYSIS OF USING AN ACOUSTIC GUNSHOT LOCATOR SYSTEM

During the 2015-2016 budget process, the City Council imposed a Budget Proviso (92-2-B-1) on the
Seattle Police Department (SPD). It reads:
“Of the appropriations in the 2015 budget for the Seattle Police Department’s Field Support
Administration BCL, $250,000 may not be spent until the Seattle Police Department completes
an assessment, files a report with the City Clerk on the feasibility, advisability and costeffectiveness of implementing an acoustic gunshot locator system (AGLS) in Seattle, and
appears before the Public Safety, Civil Rights, and Technology Committee to present the
contents of the report.”

This memorandum serves as the Department’s response to the Proviso. It provides a brief overview
of AGLS technology, its performance, and addresses related privacy concerns. It also discusses the
potential use of AGLS technology, and outlines a possible partnership and funding opportunity. It
concludes that deployment of AGLS could provide a valuable resource to officers investigating shots
fired incidents.
The Technology
AGLSs use a series of microphones and sensors that are placed throughout a geographic area to
acoustically identify gunshots. AGLS is designed to detect various gun types and calibers (bullet size
and strength). Using acoustic triangulation, the systems identify gunshots from other acoustical
interference and using geographic information systems (GIS) provide an accurate location of where
the shots took place. The system communicates gunshot information or annunciations to either a
dispatch center or directly to law enforcement officers in their patrol vehicles. This includes the
ability to count of the number of shots fired during a single incident and over time in an area covered
by AGLS. Systems like ‘ShotSpotter’ can coordinate with existing video cameras in areas where the
technology is deployed, to start recording on directional or fixed cameras. It also collects enough
information about shots for forensic and intelligence analysis such as weapon type and caliber,
directional information, and other information based on time and distance between shots.
Performance
There are several rigorous evaluations of this technology for law enforcement many of which pertain
to the basic functionally of AGLS. The research shows that the systems can consistently identify
random gunshots (with 80 percent to 90 percent overall accuracy) and identify where they came
from (within about 40 feet). It does get police to the scene faster than traditional citizen reporting
and dispatching methods (reduced response time by about 1 minute) and seems to show that

 random gunfire goes largely unreported in communities (perhaps as low as 23 percent of incidents
actually reported).1
The research also shows that AGLS paired with camera technology and targeted police strategies
were more impactful on gun-related violence than the use AGLS alone.2
Privacy Concerns
As a co-sponsor of Seattle’s privacy initiative, the Department is cognizant of community concerns
related to the use of law enforcement technologies. The Department is fully supportive of the privacy
principles that have been developed and the privacy toolbox that has been recently completed. As
such, no implementation decisions will be made prior to vetting the options through the privacy
initiative. Additionally, SPD recognizes that any deployment must be made consistent with the
requirements in SMC 14.18, which has strict requirements and City Council oversight over the
acquisition of “Surveillance Equipment.” Finally, SPD is aware that significant community
engagement will be appropriate to determine where and how an AGLS should be installed and
operated.
Potential Use in Seattle
SPD tracks and analyzes shots fired as part of the SeaStat process and data-driven approach to
addressing crime and disorder. Community input and historical gunshot data would drive the
implementation and placement of the AGLS system. Due to the acoustics involved, one location may
be more appropriate than the other for deploying the technology to maximize system effectiveness.
AGLS technicians could provide better insight into making a location selection based on acoustics.
The highest concentration of shots fired incidents occur in the Central District and Rainier Valley.
Use of this type of system could complement the work currently being carried out in the Real Time
Crime Center (RTCC). Annunciations could go to the RTCC where analysts could gather additional
information while officers respond to the area. AGLS research shows that departments get better
results when there is a specially designed response to its annunciations. The SPD would couple
deployment of an AGLS system with specific policies on responding to AGLS calls.
The federal government has a national initiative where it funds four to five cities for the installation
and operation of an AGLS for a one-square mile coverage area. The SPD has an existing partnership
with the Bureau of Alcohol, Tobacco, Firearms & Explosives (AFT) related to reducing gun violence.
As part of that partnership, ATF submitted a request to be one of the field divisions to receive this
funding. An award to our local ATF office would provide the opportunity to partner in utilizing the
technology without initial technology expenditures by the City. An independent research partner
could conduct a rigorous evaluation of this technology and add to the body of evaluative literature
on the effectiveness of AGLS.
See the following research: Mares, D. & Blackburn, E. (2012, January 27). Evaluating the effectiveness of an acoustic
gunshot location system in St. Louis, MO. Policing, 6(1), 26-42.; Mazerolle, L. G., Watkins, C., Rogan, D., & Frank, J.
(December 1999). Random gunfire problems and gunshot detection systems. National Institute of Justice Research Brief.
Retrieved from https://www.ncjrs.gov/pdffiles1/nij/179274.pdf; Walkins, C., Mazerolle, L. G., Rogan, D., & Frank, J. (2002).
Technological approaches to controlling random gunfire: Results of a gunshot detection system field test. Policing, 25(2),
345-371. Retrieved from http://onlinecjdegrees.uc.edu/resources/criminal-justice-research/technological-approaches-tocontrolling-random-gunfire-results-of-a-gunshot-detection-system-field-test
2
See research in footnote #1.
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 Conclusion
The Proviso requests an assessment of the feasibility, advisability, and cost effectiveness of using
this technology in Seattle. If the privacy concerns can be addressed and properly ameliorated
through the City’s privacy initiative and SMC 14.18, deployment of AGLS could provide a valuable
resource to officers investigating shots fired incidents. It is important to partner the deployment
with clear project goals and specific policies that guide an annunciation response to realize the
documented benefits. The opportunity to benefit from the ATF implementation would be a costeffective way for the City to assess this approach. SPD would need to incur some expenses to develop
policies on how to use the tool, but would not incur the expense for the installation and other annual
cost for the technology.
The Department will be available at your request to answer any questions.
cc:
Chief Kathleen O’Toole, SPD
Deputy Chief Carmen Best, SPD
Assistant Chief Lesley Cordner, SPD
Assistant Chief Steve Wilske, SPD
Assistant Chief Robert Merner, SPD
Assistant Chief Perry Tarrant, SPD
Kate Joncas, Mayor’s Office
Scott Lindsay, Mayor’s Office
Ben Noble, CBO
Jennifer Devore, CBO
Kara Tillotson, CBO

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