https://web.archive.org/web/20190910115539/https://www.nbcnews.com/news/us-news/investigators-reasonably-confident-texas-suspect-left-anti-immigrant-screed-tipped-n1039031
Investigators are “reasonably confident” that the suspect, identified by police as Patrick Wood Crusius, 21, of Texas, posted the diatribe on the extremist online forum 8chan before the shooting.
The document was deleted from one of 8chan's forums after the shooting began, but forum users archived the post, which contained a link to a PDF version.
The note cites the Christchurch, New Zealand, mosque shooter, an anti-immigrant white supremacist who left 51 dead in March, as an inspiration. The Christchurch shooter also linked to a livestream of his attack on Facebook, and posted that link to 8chan.
Anonymous online sites have become go-to sites for mass shooters to deposit their statements of purpose before embarking on mass murder. One month after the Christchurch shooter, a copycat who killed one person at a San Diego synagogue, also left a note on 4chan, a sister site to 8chan.
Users on the 8chan forum where the note appeared frequently write about their belief in a coming race war, plus anti-immigrant, racist and anti-Semitic conspiracy theories. White nationalist literature, slogans and images are mainstays. User posts on the message board following the incident referred to the suspect as a "martyr."