A Twitter account that appeared to be associated with the gunman posted photos of the weapons used in the attack footage. The user also appears to have shared links to a manifesto around the time the shooting began.
At more than 74 pages, the document outlines a white supremacist motivation for the attack. The writer, who identifies himself as a 28-year-old white man born in Australia, quotes the so-called 14 Words, the slogan shared by white supremacists worldwide. He said that while he supported white nationalist groups, he alone had decided to carry out the attack. He described the victims as “invaders” and accused them of seeking to replace white people. He wrote about attacking two mosques, one in Linwood and one in Christchurch. He focused on the latter because it was the largest, he wrote.