A gunman fired upon a Dallas immigration field office from a nearby roof Wednesday morning, killing one detainee and critically wounding two others, before killing himself in what authorities called an indiscriminate attack on U.S. Immigration and Customs Enforcement.

All three victims were inside a van outside the facility at the time the gunman opened fire, the Department of Homeland Security said in a statement. Authorities say they found ammunition with anti-ICE messaging at the scene.

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