By Amanda Musa, Priscilla Alvarez, Leigh Waldman

(CNN) — [Breaking news top, published at 11:19 a.m. ET] Evidence that the Federal Bureau of Investigation has gathered on Wednesday’s fatal shooting at a Dallas ICE field office indicates the shooter conducted large amounts of research on ICE, ballistics and the shooting of Charlie Kirk, suggesting “a high degree of pre-attack planning,” FBI Director Kash Patel said Thursday morning on X.

Also, a handwritten note recovered in the investigation reads, according to Patel: “Hopefully this will give ICE agents real terror, to think, ‘is there a sniper with AP rounds on that roof?’”

Patel said evidence was obtained through devices, data, writings and other things obtained at the shooting site, the shooter’s body and the shooter’s residence.

Among the evidence, according to Patel:

• “The perp downloaded a document titled ‘Dallas County Office of Homeland Security & Emergency Management’ containing a list of DHS facilities.”
• “He conducted multiple searches of ballistics and the ‘Charlie Kirk Shot Video’ between 9/23-9/24.”
• “Between 8/19-8/24, he searched apps that tracked the presence of ICE agents.”
• “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?’”
• “Further accumulated evidence to this point indicates a high degree of pre-attack planning.”

[Original story, published at 10:15 a.m. ET] On any given day, people detained by US Immigration and Customs Enforcement are processed at the agency’s field office in Dallas – a rectangular, brick building tucked between a busy highway, several law offices and a luxury apartment complex.

On Wednesday morning, the unassuming building became the center of national attention when a “sniper” fired “indiscriminately” at the ICE facility from the roof of another building, leaving one detainee dead and two others seriously injured, according to the Department of Homeland Security. The shooter was found dead at the scene.

When the victims were shot, they were in a van at the facility’s sally port, a fortified entryway commonly found in prisons and on military bases, DHS said. Shots were fired across the length of the facility, with bullet holes found throughout the building, officials have said.

Gunshots slicing through the air from above sent visitors running for cover or peering out of their cars to investigate – some of them worried for family members inside the facility.

Investigators are now examining writings left on a bullet casing and working to determine a motive behind the shooting, which DHS Secretary Kristi Noem told CNN appears to have been carried out by “someone who is very much against our ICE officers and the work that they were doing.” It was at least the fourth instance of violence or a threat at an ICE or Customs and Border Protection facility in Texas this year.

Here’s what we know about the suspect, the victims and the investigation:

Who was the shooter?

The person investigators believe was the shooter was Joshua Jahn, according to three sources familiar with the case. He was 29, one source briefed on the investigation told CNN.

Neither local nor federal officials have formally identified the gunman.

Authorities have said the shooter was found dead at the scene, and died from a self-inflicted gunshot wound, according to Noem.

Jahn had lived in a Dallas suburb and was charged a decade ago with delivering marijuana, according to court records.

In 2016, when he was 19, Jahn was charged with delivering more than one-fourth of an ounce of marijuana, according to Collin County court records. He pleaded guilty and the case against him was deferred, with Jahn being placed on probation.

The charge is classified in Texas law as a “state jail felony,” the least severe type of felony in the state.

In late 2017, Jahn drove cross-country to work a minimum-wage job harvesting marijuana for several months, Ryan Sanderson, owner of a legal cannabis farm in Washington state, told The Associated Press.

“He’s a young kid, a thousand miles from home, didn’t really seem to have any direction, living out of his car at such a young age,” Sanderson told the AP.

A spokesperson for Collin College in the Dallas suburb of McKinney told the AP via email that a Joshua Jahn studied there “at various times” between 2013 and 2018.

Jahn voted in the Democratic primary in March 2020 and hasn’t voted since then, according to records provided to CNN by the Collin County Elections Department. Voters in Texas don’t declare a political party when registering to vote but choose a party’s ballot when voting in primaries.

Who are the victims?

The three people shot while detained at the Dallas field office had been arrested and were awaiting transfer to a longer-term facility, ICE Deputy Director Madison Sheahan told Fox News.

DHS said they were shot while in a van in the sally port, which is the facility’s controlled entry point. This is an area where agents typically will bring in detainees, ICE Acting Director Todd Lyons told Fox News.

Authorities have not named the victims. They were in the country illegally, Sheahan said.

One of the injured detainees is a Mexican national, according to a statement from Mexico’s Ministry of Foreign Affairs.

The ministry said the head of its North American Unit expressed concern for the wounded Mexican national and requested clarification of the shooting’s events and unrestricted access to the person, the statement reads.

While DHS called the shooting “an attack on ICE law enforcement,” none of the people shot were members of law enforcement, FBI Dallas Special Agent in Charge Joe Rothrock noted during a news conference Wednesday.

Have authorities revealed a motive?

A motive for the shooting has not been identified, though FBI Director Kash Patel said “an initial review of the evidence shows an ideological motive behind this attack.”

The FBI director shared a photo of shell casings he said were found at the scene, including one with “ANTI-ICE” written on it with blue ink.

Noem told CNN the shooter was not trying to target a specific area of the facility.

“We know that there was bullet holes all over the building. It wasn’t just targeted at one specific area or through a window,” Noem said, adding that the shooter “was very much focused on hitting anyone that he could inside and making sure that they were victims of this attack.”

Rothrock said the shooting is being probed as “an act of targeted violence.”

President Donald Trump and other Republicans have blamed the left for violence, referencing the photo Patel shared.

“This violence is the result of the Radical Left Democrats constantly demonizing Law Enforcement, calling for ICE to be demolished, and comparing ICE Officers to ‘Nazis’,” Trump wrote on Truth Social.

Vice President JD Vance also claimed — without evidence — that the attack was politically motivated.

“There’s some evidence that we have that’s not yet public, but we know this person was politically motivated,” Vance said.

Where does the investigation stand?

Investigators spent the remainder of the day scouring the scene of the shooting for evidence, video shows.

Several law enforcement officers were seen standing on the roof of a building neighboring the Dallas field office, aerial video captured by CNN affiliate KTVT on Wednesday shows. The video later pans to show an aerial view of the ICE facility.

A CNN team later recorded video of authorities searching a Toyota at an office building near the field office. The team witnessed a heavy law enforcement presence at the building as authorities searched the car with Texas plates.

One side of the car displayed a map of the United States with the wording “Radioactive fallout from nuclear detonations have passed over these areas more than 2x since 1951.”

The car was cleared by the local bomb squad and other investigators before they started their search, according to a law enforcement source familiar with the investigation.

The source said investigators are also executing search warrants where they believe the shooter lived in the suburbs outside of Dallas.

It is not immediately clear what connection the vehicle has to the shooting investigation.

Who is detained at the facility?

Detainees are typically held at the field office for a short period of time during processing before they are transferred to a detention center, according to a former senior ICE official. The building contains three or four holding cells, the official said.

More than 8,000 detainees have been temporarily held at the facility over the first six months of the Trump administration, according to a CNN analysis of ICE data obtained by the Deportation Data Project, a research group associated with the UC Berkeley School of Law.

On average, detainees stayed about 14 hours in the Dallas office, according to the data, which runs through late July.

CNN reported earlier this month that ICE has kept detainees for days or longer in some hold rooms around the country.

A longstanding ICE policy restricted the agency from keeping detainees in hold rooms for more than 12 hours, but the agency amended that in June to allow stays of up to 72 hours in hold room facilities like the Dallas field office.

People who were detained at the facility have been moved to a different Texas detention center to complete processing, according to George Rodriguez, an immigration attorney and ICE liaison for the American Immigration Lawyers Association.

Meanwhile, Texas Gov. Greg Abbott said agencies will continue to “arrest, detain, and deport any individuals in this country illegally — without interruption.”

This story has been updated.

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