The House Committee on Homeland Security subpoenaed Jim Watkins, the owner of the far-right internet message board 8chan, as part of a probe into the social media site’s connections to extremists.

“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,” committee chair Bennie Thompson of Mississippi and ranking GOP member Mike Rogers of Alabama 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. Receiving testimony from Mr. Watkins is critical to our oversight on this matter.”

Watkins, who acquired the website in 2016, has been ordered to appear before the committee on Sept. 5, according to the subpoena.

8chan has been online and offline in recent days since its biggest internet service provider, Cloudflare, stopped doing business with it.

Authorities believe that the suspect in the El Paso mass shooting, Patrick Crusius, 21, posted an anti-immigrant diatribe on the website before the attack, which left 22 dead.

Watkins, an American who has lived in the Philippines, has been in contact with the committee, according to Adam Comis, spokesman for Thompson, NBC News reported.

“We believe a subpoena was the best course of action to receive testimony in a timely manner and because his primary residence is outside the US,” Comis told the network.