The sniper who opened fire on an Immigration and Customs Enforcement field office in Dallas left behind notes saying he acted alone in an attack intended to kill and "terrorize" ICE agents, whose work he viewed as "human trafficking," officials said on Thursday.

Although one person held in ICE custody was killed and two other detainees were critically wounded in Wednesday's bloodshed, it seemed clear from the gunman's writings "he did not intend to kill detainees or harm them," Nancy Larson, acting U.S. attorney for the Northern District of Texas, said at a news conference.

No government personnel were injured in the incident, though officials said ICE agents and other federal officers rushed into harm's way to save some detainees sitting helpless in transport vans while shots were being fired.

The perpetrator was found dead from a self-inflicted gunshot on the rooftop of a nearby building from which he fired on the ICE building and transport vans parked in its entryway with a bolt-action rifle, officials said. The weapon was legally purchased by the gunman in August, according to authorities.

The suspect was identified on Wednesday as Joshua Jahn, 29, a Dallas-area resident who previously attended a community college and had worked as a solar panel installer. He had climbed to his rooftop sniper's perch using a ladder carried to the scene atop his car, Larson said.

His writings were discovered during a search of his home in Fairview, Texas, Larson told reporters.

"Yes, it was just me and my brain," she quoted one of his notes as saying, adding the messages showed a "game plan" for the attack.

'VERY DEFINITION OF TERRORISM'

"He hoped his actions would terrorize ICE employees and interfere with their work, which he called human trafficking," the prosecutor said. "What he did is the very definition of terrorism."

Joseph Rothrock, special agent in charge of the FBI field office in Dallas, said all indications were that the shooter "committed this act alone," as stated in his own words.

"His handwritten notes show he did not expect to survive this event," Rothrock said.

President Donald Trump and others in his administration say the incident proves an increase in vitriolic rhetoric directed against ICE, the primary enforcement agency of Trump's aggressive immigration crackdown, is putting law enforcement at greater risk.

They also cast blame on the availability of apps capable of tracking the location of ICE agents.

"It's no different than giving a hit man the location of their intended target, and this is exactly what we saw happen in Dallas yesterday," Marcos Charles, an ICE executive associate director, said at Thursday's briefing.

According to FBI officials, Jahn used ICE-tracking apps and downloaded a list of local U.S. Department of Homeland Security facilities in preparation for Wednesday's pre-dawn attack.

The suspect also had researched video of conservative activist Charlie Kirk's highly publicized assassination, FBI Director Kash Patel said on social media on Thursday. The investigation thus far, Patel said, "indicates a high degree of pre-attack planning."

One of the first glimmers of the gunman's motives to be made public was a photo the FBI released within hours of the shooting of an unused bullet found inscribed with the phrase "ANTI-ICE."

ESCALATING VIOLENCE

Wednesday's attack was the third shooting this year in Texas at a DHS facility. A police officer was shot in July at an ICE detention center in Prairieland, and a Michigan man was shot dead by agents after opening fire on a U.S. Border Patrol station in McAllen in July.

ICE officers nationwide have been subjected to a 1,000% increase in assaults stoked by "violent rhetoric," Charles said, "and it has to stop."

The latest shooting came two weeks after Kirk, co-founder of the conservative student political group Turning Point USA and a close ally of Trump, was shot dead by a rooftop sniper during a speaking event in Utah, fueling fears of a new wave of violence in the United States.

On his Truth Social platform, Trump accused "Radical Left Democrats" of stoking anti-ICE violence by "constantly demonizing Law Enforcement, calling for ICE to be demolished, and comparing ICE Officers to Nazis."

On Thursday, Trump signed a presidential memo seeking to crack down on what he has characterized as organized efforts by left-wing groups to commit or incite political violence.

In the case of Jahn and Wednesday's shooting, investigators have found "no evidence of membership in any specific group or entity," Larson said.

Reuters reported in August that some ICE officers worried about safety as the Trump administration pushed the agency to dramatically increase arrests.

DHS spokesperson Tricia McLaughlin said in a statement on Thursday that ICE would increase security at facilities across the country.