A gunman armed with a rifle opened fire on a United States Immigration and Customs Enforcement (ICE) facility in Dallas on Wednesday, killing one detainee and critically wounding two others before taking his own life, authorities said.Officials reported that the shooter left behind ammunition marked with the phrase “ANTI-ICE” written in blue. The FBI is investigating the attack as an act of targeted violence. Acting ICE director Todd Lyons confirmed that the suspect identified was a man named Joshua Jahn.The shooting comes at a time when ICE has emerged as the sword arm of US President Donald Trump’s attempts to deport not only undocumented migrants but also legal migrants seen as critical of his administration’s priorities – including for opposing Israel’s war on Gaza.The attack on the ICE facility also comes two weeks after the assassination of conservative political activist Charlie Kirk, an event that led Trump to promise action against what he called “left-wing extremists”.Here is what you need to know:What happened and when?Police said they got a call about a shooting at about 6:40am local time (11:40 GMT) on Wednesday, September 24.Four people were shot. One detainee died, and two others were taken to hospital in critical condition.The gunman – authorities described him as a “sniper” – died from a self-inflicted gunshot. Officials said he fired indiscriminately at the ICE building from a nearby rooftop. The victims were either inside a van near the entrance to the building or nearby.Authorities “found bullets throughout the entire building that had punctured into the facility”, ICE deputy director Madison Sheahan said.A broken window is seen in this picture released on social media by Assistant Secretary for Public Affairs Tricia McLaughlin [@TriciaOhio via Reuters]No police officers were hurt, according to FBI Dallas Special Agent in Charge Joe Rothrock.The exact motivation for the attack was not immediately known. Still, FBI director Kash Patel described the attack as “politically motivated”.“These despicable, politically motivated attacks against law enforcement are not a one-off,” Patel said in a social media post.“We are only miles from Prairieland, Texas where just two months ago an individual ambushed a separate ICE facility targeting their officers.” On July 4, ICE said nearly a dozen individuals armed with tactical gear and weapons attacked its Prairieland facility, injuring an officer, who survived.What is ICE?ICE, or US Immigration and Customs Enforcement, is a federal agency under the Department of Homeland Security that enforces immigration laws – including arresting and deporting undocumented migrants – and investigates crimes such as human trafficking, drug smuggling and financial fraud.In recent years, the agency has frequently clashed with protesters, particularly over detention conditions and deportation policies.“The Department of Homeland Security reports assaults against its officers have risen eightfold since Trump began his mass deportations,” Al Jazeera’s Heidi Zhou-Castro reported from Washington.Trump has made immigration enforcement a centrepiece of his presidency, with large-scale deportations and high-profile crackdowns.“Now, the agency is deploying more security to its offices – while leaders warn that the US is headed in a dangerous direction if the political violence continues,” she added.Where did the shooting happen?The shooting took place at ICE’s field office in Dallas, which covers Texas and Oklahoma.The ICE facility sits along Interstate 35 East, just southwest of Dallas Love Field, a major airport for the Dallas-Fort Worth area, and only a few blocks from hotels that serve travellers.This wasn’t the first time the facility had been targeted.Last month, 36-year-old US citizen Bratton Dean Wilkinson was arrested after arriving at the facility and claiming he had a bomb in his backpack, showing officers what he said was a detonator on his wrist.