Recent mass shootings in Christchurch, Poway, and El Paso, as well as the lesser-known attack on a synagogue in Halle, Germany all have something in common other than being acts of violence. The perpetrators all had an online presence on a forum known as "8chan".
After the El Paso attack, 8chan was dropped by service providers and went offline. The shooter in Halle couldn't announce the attack on the forum; however, it was still live-streamed, similar to the attack in Christchurch. The attacker also used the name "anon", short for anonymous, a typical username used for privacy in forums such as 8chan.
8Chan has since rebranded as "8kun" and is back online as of November 3rd, 2019. The screenshot below shows 8kun's landing page in TOR.
Forums such as 8kun are not only a gathering place for users to gain inspiration to commit attacks. They also serve as dissemination points for manifestos furthering the spread of this type of terrorism.