The man accused of opening fire at a Dallas Immigration and Customs Enforcement field office on Wednesday, killing one detainee and wounding two others, has been identified as 29-year-old Joshua Jahn, according to officials.

Jahn, a U.S. citizen from Fairview, Texas, died from a self-inflicted gunshot wound, authorities said.

He "very likely" acted alone and "indicated he did not expect to survive the attack," officials said during a press conference on Thursday.

The weapon allegedly used in the attack
Jahn used an 8 mm bolt-action rifle in the shooting, officials said during a press conference on Thursday.

The suspect had purchased the weapon legally in August, according to Joe Rothrock, the special agent in charge of the Dallas FBI field office.

Suspect allegedly left behind note about ICE
FBI Director Kash Patel posted that Jahn allegedly left a handwritten note that read, "Hopefully this will give ICE agents real terror, to think, 'is there a sniper with AP rounds on that roof?" -- referring to armor-piercing bullets.

FBI officials previously said rounds found near the suspect contained "messages that are anti-ICE in nature."

Patel released an image of recovered shell casings, including one that had been engraved with the phrase "ANTI ICE," he said.