The FBI is investigating a shooting at an Immigration and Customs Enforcement field office on Wednesday morning in Dallas as an act of “targeted violence.”

Three illegal immigrants in federal custody were shot in a sniper-style attack, in what authorities described as a shooting that appeared to have been aimed at ICE officers, not detainees. One detainee was killed and two others are critically wounded, according to the Department of Homeland Security.

DHS had previously stated that two detainees were killed, but corrected itself in a press release on Wednesday afternoon. The suspected gunman died from a self-inflicted wound, according to authorities.