The gunman who opened fire on an Immigration and Customs Enforcement facility in Dallas hated the U.S. government and wanted to incite terror by killing federal agents, officials said Thursday, offering the first hint of a motive in the attack.

The shooting at daybreak Wednesday targeted the ICE building, including a van in a gated entryway that held detainees. One detainee was killed, and two other were critically wounded. No ICE personnel were hurt.

The gunman, who fatally shot himself, “carried out a targeted, ambush-style attack on law enforcement,” said Joseph Rothrock, the agent in charge of the FBI Dallas field office. He ”specifically intended to kill ICE agents," firing at ICE vehicles and sending multiple shots into "the windows of the office building where numerous ICE employees do their jobs every day.”

The assailant appeared to have acted alone. Nancy Larson, the acting U.S. attorney for the Northern District of Texas, said investigators found a collection of notes at his residence. One of them said, “Yes, it was just me.” Other notes were sharply critical of ICE agents and indicated he hoped to avoid hurting any detainees.

Investigators have not found that the gunman was a member of any particular group or entity, Larson said. And while he broadly wrote about hatred of the federal government, he did not mention any federal agencies other than ICE, she said.

The shooter also left behind a note saying that he hoped the attack would “give ICE agents real terror,” the FBI Director Kash Patel said on the social platform X.

The gunman, who authorities said fired indiscriminately from a nearby rooftop, was involved in a “high degree of pre-attack planning," Patel said, and agents have seized electronic devices, handwritten notes and other evidence from a Dallas-area home.

The gunman had also downloaded a document titled “Dallas County Office of Homeland Security & Emergency Management” containing a list of Homeland Security facilities, Patel said.

Hours before the shooting, the assailant conducted multiple internet searches for ballistics information and video of the assassination of conservative activist Charlie Kirk on a Utah university campus this month, Patel said. Last month, the man searched for apps that tracked the presence of ICE agents, he added.

Joshua Jahn, 29, was identified as the shooter by a law enforcement official who could not publicly disclose details of the investigation and spoke to The Associated Press on condition of anonymity.