Permanent project revision
Revision 2026-08-20-source-dates · effective 2026-07-26
Superseded. A later revision exists: 2026-08-23-full-claim-array →
Created the first structured Evidence Passport with 1 claim and 11 source dossiers.
sha256:42e934706bd65cd92d33257e68f96f37d8e98149032d02e0f3b0946977b2c4f6
add /evidencePassport — Added claim-level evidence mapping and source dossiers.add /revisionHistory — Established a permanent, hash-addressed baseline revision.The text below is copied verbatim from the published record. Each claim names the source dossiers that carry it; caveats stay attached to the claim they qualify.
clm-9c418f45784ff3c0
quantitative
The Chicago Office of Inspector General reviewed every alert from 1 January 2020 to 31 May 2021: of 50,176 alerts confirmed as probable gunshots, 41,830 recorded a disposition, and 4,556 of those found evidence of a gun-related offence — 9.1% of police responses.
This layer records what is known about each source, what is still missing, and the exact snapshot this page is rendering. A missing date, archive or hash stays visible as missing.
Awaiting operator and domain-expert review; publication of this revision implies neither.
sha256:42e934706bd65cd92d33257e68f96f37d8e98149032d02e0f3b0946977b2c4f6
src-f9592ff4f373e5c1The load-bearing document. Verbatim: 'A total of 50,176 ShotSpotter alerts were confirmed as probable gunshots'; 'a total of 4,556 indicate that evidence of a gun-related criminal offense was found, representing 9.1% of CPD responses'; 'at least one investigatory stop is documented under a matching event number in 2.1% of all CPD responses.' Also dates the contract: '$33 million, three-year contract with ShotSpotter began on August 20, 2018', extended in December 2020 to 19 August 2023. The OIG states its own data were incomplete and irreconcilable. Caution for a future check: the report PDF did not yield machine-readable text in this review, so these figures are quoted from the OIG's release page rather than the PDF body.
src-7fc294f6449adc69The report itself, for readers who want the methodology and the four recommendations. 985 KB.
src-e94b7add9160654dThe independent quantitative evaluation, and the reason the entry does not simply repeat advocacy figures. Chicago sample: 85,572 incidents, 6 February 2017 to the end of 2019. Note for anyone reusing it: the frequently quoted procedural gains — alerts arriving 93 seconds before 911 calls, locations about 300 feet closer — are the KANSAS CITY results in this study and are not Chicago findings.
src-9b9f7c3c262b943aPlain-language account of the same evaluation by its lead author, Eric Piza. Carrying sentence: 'Gun violence did not reduce in either (Kansas City or Chicago) following the introduction of ShotSpotter, and shootings were not anymore likely to be solved in either city.' Piza's own site states the project also produced peer-reviewed journal articles; those were not individually verified here, which is why this entry is graded independent rather than peer-reviewed.
src-7db747a75d032fcaLitigation-side research, published three months before the OIG audit and reaching a similar shape from different data: 1 July 2019 to 14 April 2021, 89% of deployments turned up no gun-related crime and 86% no crime report at all. Labelled here as advocacy research, not an audit — the entry's headline figure is the OIG's, not this one.
src-8ba47d02a55337b7The other side, kept in deliberately. SoundThinking argues the OIG measured the wrong thing (dispositions of police responses rather than detection accuracy) and published a separate point-by-point response to the MJC study at soundthinking.com/blog/soundthinkings-response-to-the-macarthur-justice-center-report/, plus a commissioned Edgeworth Economics critique of its methodology. The company also renamed itself from ShotSpotter, Inc. on 10 April 2023; the product kept the old name.
src-b38a7b4c822f7d07The end, with the city's own wording: 'Effective Monday, September 23, 2024, at 12:01 am, the Chicago Police Department will no longer be utilizing ShotSpotter technology', followed by a 60-day decommissioning. Mayor Johnson's stated reason: 'The ultimate goal is to deploy resources on the most effective strategies and tactics proven to accelerate the current downward trend in violent crime. We have to explore better options that save more lives.' The city's own statement page (chicago.gov, February 2024) carries the same text but returns 403 to automated fetching.
src-479b9a00a9a0d488The fight over the ending, which is not settled. The council voted 33-14 to hand contracting authority to Superintendent Larry Snelling, who supports the technology; Johnson called the ordinance illegal, Snelling did not sign over the objection of the mayor who appointed him, and the system went dark four days later.
src-ccab8aa1e59c6d22Currency check, and the reason this entry says nothing has replaced it. Twenty months after shutdown: 15 firms answered an RFI, 9 answered the RFP including SoundThinking, $13.9M sits in two budgets, no contract is awarded. Chief Procurement Officer Sharla Roberts: 'An RFP of this size, complexity and nature takes 18 to 24 months and sometimes longer to award.' A resolution filed 5 May 2026 with 35 council signatures accuses the mayor of obstruction; hearing set for 3 June 2026. A free six-month muzzle-flash pilot from Shooter Detection Systems was offered in the 9th District in January 2025; no source confirms it went live.
src-621c399c0cd79bddThe legal counterpart to the OIG's finding that the technology changed police behaviour: Chicago paid $90,000 to settle a 2022 federal suit by Daniel Ortiz and Derick Scruggs and conceded that a ShotSpotter alert alone does not justify stopping or frisking someone near the alert. Separately, the city agreed in March 2026 to pay $500,000 to Michael Williams, charged with murder in 2020 largely on an alert and held nearly a year before prosecutors dropped the case in July 2021 for lack of evidence.
src-8667325e3c20090cWhat happened after, reported here as correlation and nothing more. Police beats that had had sensors saw roughly a 32% fall in homicides between 1 January and 22 September 2025, but homicides fell about 30% citywide in 2025 to a 60-year low, including where sensors never existed. A University of Chicago analysis reported on 27 May 2026 found faster responses to top-priority 911 calls in former ShotSpotter beats, but it excluded gunfire calls from the data — a limitation critics reasonably press. Both WTTW pages return 403 to automated fetching; figures here come from search-result text and should be re-read before any figure is added to the entry body.