Patrick Crusius, a 21-year-old from Allen, Texas, was arrested shortly after the shooting and charged with capital murder.[11] Police believe a manifesto with white nationalist and anti-immigrant themes, posted on the online message board 8chan shortly before the attack, was written by Crusius; it cites the year's earlier Christchurch mosque shootings and a right-wing conspiracy theory known as the Great Replacement as motivation for the attack.[4][12][13][14]

It is the deadliest mass shooting in the United States in 2019, the seventh deadliest since 1949, and the third deadliest in Texas.[15]