Spy agencies silent on monitoring of alleged Christchurch gunman's white supremacist supporters

New Zealand's top spies won't say whether they are monitoring supporters of the alleged Christchurch terrorist - including people he has written to from prison.

The heads of the GCSB and SIS have admitted to Newshub they don't have the capability to monitor sites like 4chan - where the alleged gunman's letter was shared.

They came to Parliament on Tuesday .. but refused to answer questions about the alleged Christchurch mosque killer. 

Newshub revealed earlier this month that inappropriate letters written by the alleged Christchurch gunman were sent from prison, one included a potential call to action to white supremacist supporters.

That letter from accused gunman Brenton Tarrant was shared on 4chan. Neither of the spy bosses would confirm whether they knew about that letter before details were published by the media. 

But GSCB director-general Andrew Hampton says 4chan is simply too big to keep across everything on it.

"4chan has one million unique visitors a day, it is one of the thousand biggest websites in the world. It is a huge, huge enterprise," he said. 

In order to produce intelligence of value, you need to have some sort of lead or some sort of hypothesis. We are not constantly sucking up the whole country’s internet traffic to see who is going to which website, or who is downloading what. That is just too big an exercise.”

When it was pointed out that Newshub had been able to find a letter from the alleged gunman on the site, Hampton replied he would not discuss specifics. 

Nor would either agency confirm whether they are keeping tabs on Tarrant supporters who sent him letters. 

"We're not going to comment on that; that's a matter for Corrections," NZSIS Director-General Rebecca Kitteridge said. 

A report from the intelligence agencies released at the end of May said: "The unprecedented terrorist attacks in Christchurch on 15 March 2019 represent a significant change in New Zealand's threatscape"

But nearly six months after the attacks, neither Hampton nor the director of the Security Intelligence Service, Rebecca Kitteridge, would detail any extra actions the spy agencies were taking to monitor white supremacists.

Instead, they pointed to the Royal Commission into the Christchurch attacks.  That’s due to report back in December.