The gunman who opened fire at a U.S. Immigration and Customs Enforcement facility in Dallas, Texas, sought “real terror” for agents and “searched apps that tracked the presence” of ICE personnel, FBI Director Kash Patel revealed Thursday.

Joshua Jahn, 29, was identified by sources familiar with the investigation as the shooter who fired from a rooftop toward the ICE facility, killing one detainee and injuring two others. The shooter died after turning the gun on himself, authorities said.

“FBI Dallas and FBI HQ have been working 24/7 to seize devices, exploit data, and process writings obtained on location and in the subject’s person/residence/bedroom,” Patel wrote on X. “One of the handwritten notes recovered read, ‘Hopefully this will give ICE agents real terror, to think, ’is there a sniper with AP [armor-piercing] rounds on that roof?'”

Patel also said that the gunman searched for videos of Charlie Kirk’s assassination in Utah leading up to the attack in Dallas on Wednesday.

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“He conducted multiple searches of ballistics and the ‘Charlie Kirk Shot Video’ between 9/23-9/24,” Patel wrote. “Between 8/19-8/24, he searched apps that tracked the presence of ICE agents.”

Patel also said the shooter “downloaded a document titled ‘Dallas County Office of Homeland Security & Emergency Management’ containing a list of DHS [Department of Homeland Security] facilities.”

“Further accumulated evidence to this point indicates a high degree of pre-attack planning,” the FBI director said.

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From a nearby rooftop, Jahn allegedly fired “indiscriminately” at the ICE building, as well as at a van in the sally port where the victims were shot, the DHS said.

The three detainees were in an unmarked transport van when they were shot, before Jahn took his own life around 7 a.m., according to sources. Authorities said the gunman was found dead with a rifle on a nearby rooftop. 

A photo posted on X by Patel showed what appeared to be rifle-caliber ammunition affixed to a clip. The rounds were engraved with an “anti-ICE” message, Patel said.

Fox News’ Louis Casiano and John Roberts contributed to this report.