The shooter who carried out a “targeted” strike against federal law enforcement at a U.S. Immigration and Customs Enforcement facility in Dallas this week put considerable planning into the attack, according to the FBI.

FBI Director Kash Patel disclosed on Thursday, just a day after the attack, that the deceased suspect gunman, Joshua Jahn, had hoped the shooting would “give ICE agents real terror” and put a “high degree of pre-attack planning” into it.

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In a post, Patel outlined what police had uncovered as they worked through the night to trace Jahn’s digital footprint, as well as evidence left behind at his home and on his body about what he had planned to carry out on Wednesday morning.

Jahn had downloaded a government document known as the “Dallas County Office of Homeland Security & Emergency Management,” which listed all federal Department of Homeland Security facilities in the region, including those used by ICE, U.S. Citizenship and Immigration Services, Federal Emergency Management Agency, and U.S. Customs and Border Protection.

As far back as Aug. 19, he began to search phone apps that tracked where ICE officers were last seen on the ground. Since President Donald Trump ordered ICE in January to carry out the “largest-ever” deportation in national history, protesters have created digital platforms to share ICE’s current locations when they are making arrests in public.

A note left behind showed that Jahn hoped his attack would make ICE employees fearful.

“One of the handwritten notes recovered read, ‘Hopefully this will give ICE agents real terror, to think, ‘ is there a sniper with AP rounds on that roof?”” Patel wrote in a post on X.

AP rounds stand for armor-piercing rounds, or ammunition that can go through bulletproof vests, which ICE personnel wear when out in public.

Jahn “conducted multiple searches of ballistics and the ‘Charlie Kirk Shot Video'” on Tuesday and Wednesday morning, before he carried out his own attack.

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One person was killed and two were injured after the gunman opened fire from a nearby rooftop at the ICE office. The victims were identified as illegal immigrants who were being escorted by ICE. No law enforcement officers were struck.

The Department of Homeland Security is racing to expand security at all ICE facilities nationwide following recent attacks against personnel.