The El Paso shooter along with the gunman accused of killing 51 worshippers at a New Zealand mosque and the man accused of terrorising a synagogue in Poway, California, all posted hateful screeds on 8chan before committing their crimes.
The US Congress subpoenaed the owner of 8chan Wednesday, 11 days after a Texas man posted a racist screed on the website just before massacring 22 people in El Paso.
The House Committee on Homeland Security demanded website owner Jim Watkins testify before it on September 5 as part of work on how to counter extremist content online.
The site has become known for carrying content and discussions from the far right.
So far this year, the manifestos from three mass shooters have been posted on 8chan: the white supremacist who slaughtered 51 at mosques in New Zealand, an anti-Semitic man who attacked a California synagogue, killing one, and the El Paso gunman, who targeted Hispanics.
"In recent years, violent extremist content has proliferated on both large and small social media platforms. At least three acts of deadly white supremacist extremist violence have been linked to 8chan in the last six months," the committee said in a statement.
"We have questions on what is being done to counter this trend so we can be sure it is being properly addressed."
The subpoena was issued after Watkins indicated to the committee that he would not testify voluntarily in person.
"I am always available to talk to you by telephone," he told the committee in an email posted on 8chan's Twitter account on August 6.
Watkins, a US citizen who lives in the Philippines, defended the website last week, attacking efforts to shut it down by denying it a host online, and insisting it had not broken any laws.
"It is actually sinister behaviour. Ours is one of the last independent companies that offer a place you may write down your thoughts free from having to worry about whether they are offensive to one group or another," he said in a video uploaded to YouTube.
8chan – the "8" originally from the mathematical symbol for infinity – is popular with right-wing extremists, misogynists and conspiracy theorists.
Patrick Crusius, the 21-year-old who attacked an El Paso Walmart on August 3, posted a long statement on 8chan attacking non-whites and racial mixing.
Both he and the Poway murderer made reference to the Christchurch killer and his 8chan-posted manifesto.