Officer Sam Lopez turns away protesters near the Northwest Detention Center on Saturday in Tacoma, Wash. (Rebekah Welch/Seattle Times/AP)

A man fatally shot by police Saturday after allegedly throwing “incendiary objects” at an immigration detention center in Washington state was an anarchist who claimed association with antifascists — known as antifa — according to new details released by police.

Detectives are reviewing a manifesto written and distributed by 69-year-old Willem Van Spronsen, who police said once belonged to the Puget Sound John Brown Gun Club, a self-proclaimed “anti-fascist, anti-racist, pro-worker organization.” Officers were not aware of the manifesto before the attack on the Northwest Detention Center in Tacoma, police said in a statement Thursday.

Van Spronsen, of Washington’s Vashon Island, was also embroiled in a custody dispute with his ex-wife when he allegedly tried to blow up the privately owned detention facility, according to police. He was arrested last year at a protest at the center, court records show.

Van Spronsen allegedly approached the center around 4 a.m. Saturday, manipulating what looked like an AR-15-style rifle and setting fire to a building owned by the detention center. Police said surveillance video shows he placed flares strategically — including underneath a 500-gallon propane tank — ignited his own car so it would explode and threw molotov cocktails at nearby buildings.

As sirens signaled officers were headed to the center, where a peaceful protest had occurred eight hours earlier, police said Van Spronsen continued attacking the complex. He pointed a rifle at the four officers who arrived, police said, and refused orders to drop the gun.

The officers fired at Van Spronsen, hitting him twice and killing him, according to police.

Tacoma police identified the officers at the scene as Sgt. C. Martin, Officer J. Correa, Officer E. Allman and Officer W. Gustason, although police did not specify which officers fired their weapons. The officers were not injured, and “medical aid was staged” nearby, according to police.

The officers — with experience on the Tacoma police force ranging from nine months to 20 years — have been put on paid administrative leave, according to department policy.

Police Chief Don Ramsdell praised the officers’ actions as “honorable and courageous.”

“Because of our officers’ selfless commitment to protect and serve, countless lives were potentially saved, including the lives of employees, as well as detainees of the Northwest Detention facility,” Ramsdell said in a statement.

Police said that they were continuing to investigate the incident and that citizens and police employees would conduct an internal review after the investigation is complete.

“This could have resulted in the mass murder of staff and detainees housed at the facility, had he been successful at setting the tank ablaze,” Shawn Fallah, who heads U.S. Immigration and Customs Enforcement’s Office of Professional Responsibility, said in a statement. “These are the kinds of incidents that keep you up at night.”

No ICE employees or detainees were hurt, agency spokeswoman Tanya Roman told The Washington Post. The detention center canceled visitations for the day but did not go into lockdown, Roman said.

The attack came as thousands protested at ICE facilities nationwide ahead of the agency’s announced plans for mass arrests of undocumented immigrants Sunday. Although the Trump administration said it would target about 2,000 families for deportation in as many as 10 cities, large-scale enforcement operations failed to materialize.

The Northwest Detention Center on the Tacoma Tideflats is owned and operated for ICE by a private company called the Geo Group, according to the Northwest Immigrant Rights Project, which puts the facility’s capacity at 1,575 — making it one of the biggest immigration detention centers in the country, the group says. As ICE faces calls to improve conditions for migrants in its custody, some have called on the government to stop using privately run detention centers.

Geo Group spokesman Pablo Paez told The Post that the company is concerned that “outrageous and baseless accusations that have been leveled against our facilities have led to misplaced aggression and a dangerous environment for our employees.”

“Contrary to the images of other facilities on the news, our facilities have never been overcrowded, nor have they ever housed unaccompanied minors,” Paez said in a statement.

Van Spronsen was arrested at the Tacoma facility in June 2018, court documents show, amid what a prosecutor described as a noisy protest scene that included yelling, banging on pots and pans, using megaphones and honking horns.

In that incident, Van Spronsen lunged at a police officer who was detaining a fellow protester at the center, according to a prosecutor’s written account. Van Spronsen allegedly wrapped his arms around the officer’s neck and shoulders to free the 17-year-old being held.

Van Spronsen was escorted away through dozens of screaming protesters, the prosecutor wrote. Officers took a baton and a folding knife the man had been carrying.

He pleaded guilty to obstructing a law enforcement officer, court records show.

Deb Bartley, who said she was a longtime friend of Van Spronsen’s, told the Seattle Times she believes he intended to die by attacking the detention center Saturday.

“He was ready to end it,” she told the Times. “I think this was a suicide. But then he was able to kind of do it in a way that spoke to his political beliefs. . . . I know he went down there knowing he was going to die.”

Bartley said Van Spronsen wrote letters to her and others “saying goodbye."

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