(CNN) - New Zealand's prison authority has acknowledged it made a mistake in allowing the alleged Christchurch mosque attacker to send a letter, which then surfaced on 4chan, an online message board known for hosting the views of white supremacists.
"I have no concern about myself and I only worry for Europe's future," Tarrant wrote.
The letter was sent to an address in Russia, a country which Tarrant also wrote at length about, before it was posted to 4chan.
"We have made changes to the management of this prisoner's mail to ensure that our robust processes are as effective as we need them to be."
Tarrant is accused of carrying out the March 15 attacks on two Christchurch mosques, in which 51 people were killed.