The 69-year-old armed man killed by Washington state police as he attacked a local Immigration and Customs Enforcement detention center Saturday sent a manifesto to friends the day before the assault in which he wrote "I am Antifa," and was being lionized by members of the leftwing group as a "martyr."

The group Seattle Antifascist Action described assailant Willem Van Spronsen a "good friend and comrade" who "took a stand against the fascist detention center in Tacoma" and "became a martyr who gave his life to the struggle against fascism."

"He was kind and deeply loved by many communities; we cannot let his death go unanswered," the group wrote in a Saturday Facebook post. "Throughout history we idolize figures like John Brown for their courage to take the ultimate stand against oppression, and today we stand strong in our support for yet another martyr in the struggle against fascism. May his death serve as a call to protest and direct action."

Friends of the 69-year-old have defended him in the attack's aftermath, accusing police of murdering Van Spronsen. Deanne English told KIRO7 she last saw Van Spronsen outside the facility, which was the site of an earlier protest, Friday night.

"And he was probably just standing his ground," she told the television station about his death. "Because that's what he does."

Another friend, Deb Bartley, told the Seattle Times, however, that Van Spronsen was an anarchist and anti-fascist who, she believed, attacked the detention center intending to provoke a fatal conflict.

Van Spronsen was armed with a rifle and incendiary devices when he launched his assault on the Northwest Detention Center in Tacoma around 4 a.m. Saturday, according to the Tacoma Police Department. Employees reported he was throwing 'incendiary devices' and setting vehicles on fire and the first officers on the scene said he was wearing a sachet and carrying flares.

Van Spronsen was trying to ignite a propane tank when he was confronted by the officers, who opened fire. The Pierce County Medical Examiner’s office said he died of multiple gunshot wounds.

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Several friends of Van Spronsen said they received a manifesto from him Friday calling the facility "an abomination" and asking "those burdened with the wreckage from my actions" to "make the best use of that burden."

In the manifesto, obtained by KIRO7, Van Spronsen said he wanted to make a statement at the facility.

"I regret that I will miss the rest of the revolution," he wrote. "Doing what I can to help defend my precious and wondrous people is an experience too rich to describe. I am Antifa."

Bartley told the Times she and other friends of Van Spronsen got letters in the mail "just saying goodbye," in addition to the manifesto.

"I regret that I will miss the rest of the revolution. Doing what I can to help defend my precious and wondrous people is an experience too rich to describe. I am Antifa." — Willem Van Spronsen's manifesto obtained by KIRO7

"He was ready to end it," Bartley said. "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."

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Van Spronsen was arrested last year for assaulting a police officer during a June 26 protest outside the same detention center, according to court records.

According to court documents, he lunged at a cop and wrapped his arms around the officer's neck and shoulders while the officer was trying to detain a 17-year-old protester, The News Tribune reported. When police handcuffed Van Spronsen they found he had a collapsible baton and a folding knife in his pocket, according to court documents.

Van Spronsen pleaded guilty to a charge of obstructing police and was released from custody in October.

Demonstrators returned to the Tacoma facility -- where bullet holes from Van Spronsen's attack were still visible -- to protest ICE immigration roundups that began over the weekend.

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The facility, privately operated by the GEO Group on behalf of ICE, holds illegal immigrants pending deportation proceedings. The detention center has also held immigration-seeking parents separated from their children under President Trump's "zero tolerance" policy, an effort meant to deter illegal immigration.

The Florida-based company told Q13 News in a statement they blamed a "factually inaccurate portrayal" of their detention centers for spurring "misplaced aggression and a dangerous environment for our employees."

"Violence of any kind against our employees and property will not be tolerated," the company stated.

The Tacoma Police Department said four officers were involved in the shooting and all have been placed on paid administrative leave, per department policy. Authorities have not released additional information about Van Spronsen.

Fox News' Sam Dorman and the Associated Press contributed to this report.