The man suspected of shooting at the Immigration and Customs Enforcement building in Dallas on Wednesday left a long record of himself online but apparently little indication that he was politically active.

Department of Homeland Security officials have called the assault on the building a direct attack on ICE agents and law enforcement officials, pointing to engravings on rounds at the scene with the phrase “ANTI-ICE” as evidence of an “ideological motive.” The suspect, identified as Joshua Jahn, 29, died of self-inflicted gunshot wounds, officials said.

President Trump condemned “Deranged Radical Leftists” in a social media post about the shooting, linking the attack to the assassination of the political activist Charlie Kirk. “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,’” he wrote.

D.H.S. officials said the suspect was targeting the ICE office from a nearby building. One detainee died in the shooting, and two others were critically wounded, officials said.

Mr. Jahn, who according to records voted in a Democratic primary in March 2020 in Texas, had an extensive online profile. But he showed little obvious interest in politics based on what has been uncovered so far. He has at least two Reddit accounts, where he talked about video games, cars, “South Park” and marijuana.

He was also registered to vote as an independent in Oklahoma, where his parents own property in Durant, Okla., north of Dallas, and where he voted once, in the 2024 general election.

Public records indicate that Mr. Jahn had at least a few minor scrapes with the law, including a charge for selling marijuana in 2015. He was released from court supervision for that charge a few years later, and the proceedings were dismissed.

Mr. Jahn was raised with a brother and a sister in a far north suburb of Dallas. His father retired in 2020 after spending 36 years in engineering roles at an elevator and escalator company, according to his LinkedIn profile.

Mr. Jahn lived with his parents in Texas at least as recently as a few months ago, according to public records. Their house is on a cul-de-sac in a rural area north of Dallas and Fort Worth that is rapidly developing as the metropolitan area expands. The house is a short drive from an outlet mall in Allen, Texas, where a shooter killed eight people in 2023.

Before noon on Wednesday, a blue truck drove quickly down the residential street leading to Mr. Jahn’s house. A man and woman got out of the car, quickly went into the house and did not answer the door.

Aric Toler, Stuart Thompson and Kitty Bennett contributed research.