An internal affairs investigation is a police department's formal inquiry into whether one of its own officers violated policy, and the decision that follows — discipline or none — is made not by prosecutors or judges but by the department's command staff, subject to union contracts, state officers' bills of rights, and sometimes arbitration. The scale of the funnel is documented: per analyses of Chicago's complaint data covering 2011 through 2015, roughly 98 percent of nearly 29,000 civilian complaints closed without any disciplinary action. Internal affairs is where accountability is supposed to happen, and the record shows it is where most accountability ends.
This article walks through the process step by step: how complaints enter, how investigators classify and resolve them, and where discipline decisions are actually made. It publishes information, not legal advice.
How does a complaint enter the system?
Complaints arrive from civilians, from other officers, or from supervisors who observe conduct. Nearly every large department now accepts complaints online, by mail, at any station, and anonymously, changes accelerated by consent decrees in cities including New Orleans and Seattle. A complaint is logged with a tracking number — a reform with real consequences, since departments that resisted numbering made cases easy to lose — then classified: internal affairs handles serious allegations, including excessive force, dishonesty, and criminal conduct, while line supervisors typically handle minor matters such as discourtesy. That classification is the first consequential decision, and complaint data reviewed under court supervision has repeatedly shown it is applied inconsistently.
What does the investigation itself look like?
Investigators interview the complainant, the accused officer, and witnesses, collect body camera footage and radio traffic, and document physical evidence. Under officers' bills of rights — statutes in more than 20 states, per the National Conference of State Legislatures' summaries — the accused officer receives procedural protections: notice of the allegations, a specified interview window, representation, and sometimes a delay before questioning after a critical incident. Investigations carry deadlines, typically 90 to 180 days, and untimely cases are often barred outright. Each rule has an origin story in due process, and each also functions in practice as a clock that complaint data shows runs out on civilian cases more often than on internal ones.
What does 'sustained' mean, and who decides?
Investigators return one of four standard findings: sustained, where the evidence shows the policy violation occurred; not sustained, where the evidence is inconclusive; exonerated, where the conduct happened but broke no policy; or unfounded, where the conduct did not occur. The standard of proof is the preponderance of the evidence in many departments, the same civil standard used in court. A sustained finding does not itself impose punishment. Discipline is decided separately — by the chief or commissioner, informed by a disciplinary matrix that suggests penalty ranges by violation and record — and in many jurisdictions is then negotiable through grievance arbitration or civil service review, where arbitrators have documented authority to reduce or erase imposed discipline.
| Stage | Decision maker | Documented pressure point |
|---|---|---|
| Classification | Intake investigators | Serious allegations downgraded to minor track, per monitor audits |
| Investigation | Internal affairs | Statutory deadlines bar late cases |
| Finding | IA command or review board | Sustain rates below 10 percent in several large departments |
| Discipline | Chief or commissioner | Union contract limits on penalty and records access |
| Final outcome | Arbitrators, civil service boards | Discipline reduced or vacated after imposition |
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Why do sustain rates run so low?
Researchers attribute low sustain rates to a combination of evidence, standard, and structure. Corroboration is often thin: a civilian's account against an officer's, in the absence of video. The standard requires proof of a specific policy violation, and policies may be written narrowly. Structurally, investigators and accused officers work in the same institution, a conflict of interest that oversight bodies and consent decree monitors have documented for decades. Chicago's figures are not an outlier: published reviews of complaint outcomes in other large departments, including Philadelphia and Baltimore during their decree and oversight periods, show sustained findings in the single digits to low teens. The number measures the system, not the truth of individual complaints, and both defenders and critics of departments agree on that reading.
Who reviews internal affairs from the outside?
Auditors, monitors, and civilian review bodies form the outside layer, and their documented power is the power to read. Chicago's decree requires an outside auditor to review completed IA investigations each year, and the first audit reports found investigation quality problems, including interviews that failed to follow up on contradictions in an officer's account. Monitor reports in New Orleans and Seattle found the same pattern in earlier years: files that closed neatly without the interviews that an outside reader would have expected. Those findings are why reform agreements target the paperwork first. An outside reader cannot force discipline, but the record shows that documentation of how investigations were handled is the one lever that has repeatedly forced departments to retrain investigators and reopen cases.
What changes have oversight bodies and consent decrees produced?
Decrees in New Orleans, Seattle, and Chicago rewrote the intake, investigation, and review stages: independent oversight of IA files, complaint-tracking systems audited by monitors, and public reporting of outcomes. New Orleans's Independent Police Monitor gained access to IA files that were previously closed. Chicago's 2019 decree required the city to publish complaint outcome data. The measurable product is visibility — data where silence stood — while the discipline decision itself remains where it has always been, in command staff hands, bounded by contracts arbitrators enforce.
Where does a fired officer go next?
Terminated officers can appeal to civil service boards or arbitration, and reinstatements are documented: arbitrators in several large cities have returned officers whose terminations followed sustained serious misconduct, decisions that generated legislative proposals in multiple states to limit arbitration of police discipline. Officers separated for cause are also supposed to be reported for decertification. Per the International Association of Directors of Law Enforcement Standards and Training, which runs the National Decertification Index, reporting by states remains voluntary and uneven, so an officer stripped of credentials in one state can, in some cases, seek employment in another. That gap, more than any single discipline decision, is where the system's seams show.
For more context, read How civilian oversight boards get power, and where they hit limits.
For more context, read police accreditation.