New Zealand media organisations have taken the unprecedented step of agreeing to limit their reporting of the trial of the man accused of the Christchurch mosque massacre in an attempt to contain the dissemination of his white supremacist beliefs.

On 15 March a shooter killed 50 people in two Christchurch mosques, the largest mass shooting in New Zealand’s modern history.

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In the lead-up to the accused shooter’s next court appearance on 14 June, New Zealand’s five largest media organisations have signed a voluntary agreement committing to adhere to a strict set of protocols designed to limit the exposure of the accused killer’s ideals and beliefs.

Brenton Tarrant, an Australian, has been charged with 50 counts of murder and 39 of attempted murder. He is being held in isolation in New Zealand’s only maximum-security prison, Paremoremo, where he has laid a complaint that his detention is breaching his human rights.

A copy of the agreement, signed by the heads of RNZ, TVNZ, Mediaworks, NZME and Stuff, says they fear the accused could use his trial “as a platform to amplify white supremacist and/or terrorist views or ideology”, and preventative action needed to be taken to limit his audience and exposure.

“We are also mindful of our role as the ‘eyes and ears of the public’ in the context of court reporting,” the agreement states.

“In this instance, we acknowledge the particular importance of this function, given the many victims’ friends and families outside New Zealand who may otherwise be unable to engage in the trial process.”

The pledges in the agreement include only assigning senior journalists to cover the trial, limiting the coverage of statements that “actively champion” white supremacist or terrorist ideals, not quoting from the accused’s manifesto, and not broadcasting or publishing “imagery, symbols or signals” from the accused that reference white supremacist ideology, including hand signals such as the Nazi salute.

It is understood the agreement is the first of its kind to be signed in New Zealand and represents a bold step forward for media co-operation during a time of unprecedented upheaval and intense competition for dwindling audience numbers.

Paul Thompson, chief executive and editor-in-chief of RNZ, New Zealand’s state broadcaster, said the speed and ease with which the agreement had been discussed and signed in the wake of the attack signified a new era of co-operation for domestic media in covering the most challenging and difficult story in the country’s history.

“I thought it was important we agreed as senior editors to be cohesive and united in terms of showing we were going to be responsible and rigorous in how we covered the trial,” said Thompson.

“We needed to signal that we would not become a platform for hate speech, for spreading hateful ideology or being a pawn in anyones game.”

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Thompson said he expected some pushback from audiences who wanted to be able to follow the trial word for word, as well as complaints from others who felt the accused deserved no publicity at all.

“This trial is going to be incredibly volatile and tricky, international media won’t be so constrained [as domestic] and social media will be the typical wild west. I think that makes it imperative that trusted news organisations do what they can to provide people with reliable information.”

Professor Anne Goldson, a lecturer in media and communications at Auckland university, praised the agreement, and said it appeared to be taking a distinctly different tack from other high-profile terrorist cases, such as the trial of Norwegian mass murderer Anders Breivik, a self-declared Nazi.

“In the Anders Breivik case they did have a pretty open process, and from what I understand he performed so poorly that it was counter-productive to his ideas. But that was probably quite a risky stance to take in terms of exposure” Goldson said.

Last week prime minister Jacinda Ardern announced she would lead a global effort to combat violent extremism and terrorism on social media, and was in discussions with tech companies such as Facebook about tightening and modifying their platforms.