The alleged gunman who targeted a U.S. Immigration and Customs Enforcement (ICE) facility in Dallas on Wednesday conducted the deadly shooting with "a high degree of pre-attack planning," FBI Director Kash Patel said on social media Thursday morning.

Patel posted a list of updates on X he said come from evidence the bureau has uncovered in the hours since the attack.

The first update was that the suspected shooter had downloaded a document from the Dallas County Office of Homeland Security and Emergency Management "containing a list of DHS facilities." 

A similar document to what Patel described is posted on the county website listing the the addresses for the ICE facility in Dallas and the U.S. Citizenship and Immigration Services office in Irving. The document appears to be a reference for people who come to the county for citizenship and immigration issues instead of the federal government.

FBI finds note, Google searches for Charlie Kirk shooting, ICE trackers

Patel also said the suspect's devices had records of him searching for information about ballistics, video of Charlie Kirk being shot and apps that tracked the presence of ICE agents.

Patel said agents found a handwritten note that read: "Hopefully this will give ICE agents real terror, to think, 'is there a sniper with AP rounds on that roof?" (AP could refer to armor-piercing or armor-penetrating rifle rounds.)

"Further accumulated evidence to this point indicates a high degree of pre-attack planning," Patel said.

On Wednesday morning, hours after the attack, Patel posted a picture of what he said were unfired rounds left at the scene, one of which had "ANTI-ICE" written on it. 

Shooting at the Dallas ICE facility

Three people at the ICE facility were hit when the shooter, identified as Joshua Jahn, opened fire on Wednesday morning. ICE's acting director told CBS News that the shooter fired "indiscriminately" into the building and vehicles stationed there. A group of detainees who had recently been picked up was inside one of the vans.

All of the victims were detainees. One of them died and the other two are in critical condition. Jahn also died of a self-inflicted gunshot wound, authorities said.

ICE has not responded to requests for any information about the victims. The Mexican Consulate in Dallas confirmed that one of the victims is a Mexican national. 

The Dallas ICE Field Office serves as a temporary holding facility for some detainees. Between January 20 and mid-June, an average of 47 people were held there each day, spending roughly seven hours in detention, according to a CBS News analysis of ICE data compiled by the Vera Institute of Justice and the Deportation Data Project.