A shooter with a rifle opened fire from a nearby roof onto a U.S. Immigration and Customs Enforcement location in Dallas on Wednesday, killing one detainee and wounding two others before taking his own life, authorities said.

The exact motivation of the attack was not immediately known. The FBI said at a morning news conference that ammunition found at the scene contained anti-ICE messaging. The head of the agency, Kash Patel, released a photo on social media that shows a bullet containing the words “ANTI-ICE” written in what appears to be marker.

See Full Page