How have prior investigations assessed federal agents’ use of tear gas and stun grenades in US protests?

1. What investigators actually looked at: sources and methods

Investigations range from nonprofit forensic reviews and academic law‑reviews to coordinated newsroom reconstructions and courtroom testimony; Physicians for Human Rights analyzed court records and declarations from Los Angeles protests, Chicago reporters compiled photographic and video evidence and tipline submissions across dozens of incidents, and law journals and human‑rights groups reviewed historical patterns and munitions mechanics to assess use and harms ^{[1] [2] [5] [6]}.

2. Core findings: patterns of indiscriminate or excessive deployment

A recurring conclusion is that federal agents deployed chemical irritants and stun grenades in ways that failed to discriminate between violent actors, peaceful protesters, journalists and bystanders — including rolling canisters into crowds, firing pepper rounds at people not posing immediate threats, and repeated, frequent uses even where video evidence showed largely nonviolent gatherings ^{[1] [2] [7]}.

3. Documented harms and medical concerns

Medical and research reviews emphasize that “less‑lethal” labels mask real risks: tear gas and similar riot‑control agents can cause severe injury and even death in some contexts, and flash‑bangs or heavy canisters carry blunt‑force or blast risk; field reporting and hospital transports (including parents and infants affected in Minneapolis) provide concrete instances of acute harm tied to these deployments ^{[1] [5] [4]}.

4. Judicial and policy responses to investigative findings

Courts and judges have responded to the investigative record: at least one federal judge extended indefinite restrictions on immigration agents’ use of tear gas, pepper balls and flashbangs, requiring warnings and limiting uses to situations where an “immediate threat” existed — a remedy explicitly grounded in witness testimony and evidence presented in filings and hearings ^{[3] [2]}.

5. Investigations’ criticisms of tactics and adherence to standards

Human‑rights organizations and academic reviews argue that federal practices often contravened international guidance and accepted policing norms — citing “gas and run” tactics, absence of adequate warnings, use in residential neighborhoods, and equipment deployments that make control and targeting impossible once agents are released ^{[1] [6] [5]}.

6. Counter‑claims, mixed evidence and agency defenses

Federal officials have publicly defended some uses of force as justified and necessary in the face of threats, and in certain high‑conflict encounters agencies have reported officer injuries — meaning investigations operate in a contested factual environment where video, witness accounts, agency statements and legal pleadings sometimes point in different directions ^{[8] [9]}.

7. Gaps, limits and what investigators could not resolve

Investigations often relied on video, witness declaration and patchwork reporting because transparency around munitions policies, unit identification, and comprehensive internal after‑action reviews is limited; several reviews explicitly note incomplete records and inconsistent labeling of chemical agents across agencies, constraining definitive causal attributions in some incidents ^{[2] [10] [5]}.

8. Practical takeaway: accountability, limits and continuing scrutiny

Taken together, prior investigations portray a pattern of problematic federal crowd‑control tactics that produced documented harms and legal pushback, while also revealing competing narratives from agencies that cite officer safety; those findings have translated into court limits and sustained demands for independent oversight, even as gaps in documentation leave some specifics unresolved ^{[3] [1] [2]}.