The White supremacist hating Muslims, who massacred two mosques, chose New Zealand to show "no place in the world was safe".
Brenton Tarrant said he moved from Australia, his homeland, to the island to "live temporarily while I was planning and training".
"But I soon discovered that New Zealand was a rich target of an environment [sic] like nowhere else in the West," wrote the 28-year-old personal trainer in his chapel titled "The Great Substitute" .
"Secondly, an attack in New Zealand would bring to light the truth that no place in the world was safe, even in the most remote parts of the world," he added.
Forty-nine people were killed when he opened fire on Friday afternoon inside the Masjid Al Noor Mosque and Linwood Masjid Mosque while the prayers were in session.
Tarrant was captured by the police.