New Zealand officials have admitted making a mistake by allowing the man accused of killing 51 people at two Christchurch mosques to send a handwritten letter from his prison cell.
The six-page letter from Brenton Tarrant was posted this week on the website 4chan, which has become notorious as a place for white supremacists to post their views.
It comes at a sensitive time, with other alleged killers from El Paso to Norway citing Tarrant as an inspiration.
The letter appears to have been written in pencil on a small notepad and is addressed to "Alan" in Russia.
Much of it appears to be relatively innocuous, discussing a one-month trip Tarrant says he took to Russia in 2015, but the letter also warns that a "great conflict" is coming and uses language that could be construed as a call to arms.
Corrections minister Kelvin Davis said he did not believe the prison system should have allowed Tarrant to send the letter.
"I have made myself clear that this cannot happen again," he said.
But Davis also said that all New Zealand prisoners have rights that include the ability to send and receive mail. He said the prison system can withhold correspondence and held some other letters Tarrant had attempted to send or receive.
"We have never had to manage a prisoner like this before - and I have asked questions around whether our laws are now fit for purpose and asked for advice on what changes we may now need to make," Davis said.
Opposition spokesman David Bennett said Davis needed to demand immediate answers about how an inflammatory letter could be sent from inside a maximum security prison.
"This man is accused of carrying out one of the most heinous crimes in New Zealand history," Bennett said.
"New Zealanders will be horrified that Corrections allowed him to send a letter which includes a call to action and has subsequently been posted online."
The Corrections Department said the law only allows a jail director to withhold an inmate's mail in a "very limited" range of circumstances.
"On review, we acknowledge that this letter should have been withheld," the department said in a statement.
Before the March 15 shootings, Tarrant, a 28-year-old Australian white supremacist, posted a 74-page manifesto on the website 8chan, a more radical offshoot of 4chan.
On the website he outlined his racist views and his beliefs that immigrants were invaders who would replace the white race.
New Zealand prime minister Jacinda Ardern has vowed never to say Tarrant's name to deny him the publicity she says he craves, making Tarrant's letter even more of an embarrassment for the government.
When news of Tarrant's letter emerged, Ms Ardern said: "I think every New Zealander would have an expectation that this individual should not be able to share his hateful message from behind bars."
Tarrant has pleaded not guilty to terrorism, murder and attempted murder charges following the mosque attacks. He remains in jail ahead of his trial, scheduled for May.