The FBI said on Thursday that the suspect in the shooting at an Immigration and Customs Enforcement (Ice) detention facility in Texas the day before had engaged in a “high degree of planning” before the attack.
The FBI director, Kash Patel, said in a statement on Thursday morning that the alleged perpetrator downloaded a document titled “Dallas County Office of Homeland Security & Emergency Management” containing a list of Department of Homeland Security (DHS) facilities.
The shooting occurred early on Wednesday at a facility in Dallas, with a spray of bullets fired from a rooftop hitting a building and an Ice transportation van, killing one Ice detainee who was inside the vehicle and badly injuring two others.
Related: Deadly Ice shooting comes as violence spikes amid Trump immigration crackdown
No Ice staff were hit in the attack, which the Trump administration condemned as being an action aimed at law enforcement and is urgently investigating, amid a surge in political violence in the US.
The suspect was identified as 29-year-old Joshua Jahn, who took his own life at the scene.
On Thursday, Patel said that the suspect had conducted multiple searches of ballistics and had searched the “Charlie Kirk Shot Video” in recent days, referring back to the murder of the rightwing activist and youth politics leader who was shot dead at an event in Utah earlier this month.
Patel also said that between 18 August and 24 August, the suspect searched apps that tracked the presence of Ice agents. The FBI director added that authorities also recovered a handwritten note which read, ‘Hopefully this will give Ice agents real terror, to think, “is there a sniper”? about to fire from a roof.”
Patel added: “Further accumulated evidence to this point indicates a high degree of pre-attack planning.”
Authorities provided more details at a news conference on Thursday afternoon and said that at around 3am on Wednesday the suspect was seen driving, on footage, with a large ladder on his car, that they believe he used to position himself on top of the building.
The shooting, authorities said, started at about 6.30am on Wednesday, and officials said on Thursday that they believe that the suspect acted alone.
Nancy Larson, acting US Attorney for the northern district of Texas, said that authorities found a collection of notes at the suspect’s residence, with one of the note notes allegedly stating: “Yes, it was just me.”
“Notably, these loose notes included a game plan of the attack and target areas at the facility,” Larson said. “He called the Ice employees: people showing up to collect a dirty paycheck.”
Larson said that the suspect “wrote that he intended to maximize lethality against Ice personnel and to maximize property damage at the facility” and said that it “seems that he did not intend to kill the detainees or harm them. It’s clear from these notes that he was targeting Ice agents and Ice personnel.
“He also hoped his actions would give Ice agents real terror of being gunned down, and he did this to induce constant stress in their lives,” Larson said.
Among his papers, Larson said that they also found a handwritten note in which the suspect “expressed his hatred for the federal government”.
The suspect who shot Kirk earlier this month also fired from a rooftop at a relatively long distance, using a high-powered rifle with a precision scope in a sniper-style attack. He fired just one bullet in an assassination-style discharge that hit Kirk in the neck. The shooter at the Ice facility fired many bullets in a much more scattered fashion that did not appear to include aiming at a specific individual.
The identities of the victims in the Dallas attack have not yet been named , although the two men wounded were said to remain in the hospital in critical condition.
The mayor of Dallas, Eric Johnson, a Democrat turned Republican, described the shooting on on CNN in a live interview on Thursday morning as “really, really sad.
“I want to stay out of the way of the FBI investigation … but I will tell you that it’s very troubling,” he said “I think the trend that we’re seeing of increasing political violence in this country, and yesterday’s … hit close to home and we’re concerned.”
Johnson added: “The division that seems to be leading to some folks taking these very, very unfortunate and violent steps to try to bring about policy changes [is] just wrong and it’s scary.”
Johnson condemned “the vilification of Ice”, the federal agency that has been stirring up protests amid the Trump administration’s anti-immigration, mass deportation agenda, with raids on immigrants across the country and a surge of detentions.
The motive of the suspect in Wednesday’s incident is still being investigated. A relative of the man said Jahn was not particularly political, NBC reported, but one unspent bullet casing was marked “Anti-Ice”.
Patel shared the developments as Donald Trump blamed the shooting on “Radical Left Terrorists” and the Democratic party, without citing official evidence of any specific affiliations, party politics or motives of the suspect.
The US president wrote on social media the day of the Dallas attack: “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.”
JD Vance made a political comment before a suspect had even been named or many details of the victims released, saying that the attack was carried out by “a violent leftwing extremist” who was “politically motivated to go after law enforcement”.