Law enforcement’s use of chemical weapons is a threat to human and environmental health, exemplified during 2020 Black Lives Matter (BLM) protests in Portland, OR, where city, county, state, and federal agencies have deployed various chemicals for over 100 days. In the second half of July, Department of Homeland Security (DHS) agents used an exceptionally toxic and unknown weapon to quell free speech in support of Black lives and against federal presence. With significant support from the community, I combined first-hand accounts, media reports, videos and photos of munitions, primary literature and analytical chemistry to identify the weapon as gaseous Zinc Chloride (ZnCl2) from so-called Hexachloroethane (HC) “smoke” grenades. I then used hierarchical Bayesian methods to estimate that DHS deployed 24 (23 - 27) HC grenades in July. The gas released is so toxic that the grenades deployed produced enough ZnCl2 to kill the author (~100 kg) 137 (131 - 154) times over and its release has led to persistent major health issues in the exposed population. Given prior case histories of ZnCl2 exposure and novel symptoms associated with HC grenade use by DHS, ZnCl2 is certainly the causal agent and has created an ongoing human and environmental health crisis extending well beyond the protests’ footprint. DHS’s wanton use of ZnCl2 against protesters will have lasting impacts for decades and was identified through a community of civilians standing up to say Black Lives Matter.