"Dear Christchurch, Breivik's trial showed us extremist ideas struggle in the light." These are the words of Norwegian journalist Åsne Seierstad, who covered the trial of Norwegian terrorist Anders Breivik.

Seierstad tells RNZ's Lately the openness of the Norwegian trial gave victims the chance to tell their stories and to learn what they needed to know about the tragedy.

"Here in Norway... the prosecutors went through every single [one] of the 77 murders.

In a piece in The Guardian, Seierstad observed the differences between the Breivik trial and the sentencing in Christchurch this week of mosque terrorist Brenton Tarrant.

While Norway opted to bring every possible detail to light during the 10-week trial of Breivik, Seierstad writes that the case against the Christchurch shooter seems "dimly lit".

Seierstad wrote the book, One of Us: The Story of Anders Breivik and the Massacre in Norway.

In 2011, Breivik detonated a bomb outside the Norwegian prime minister's office in downtown Oslo, killing eight people. He then travelled to the island of Utøya where a summer camp of Labour party youth was about to be held and shot and killed 69 people, mostly teenagers.

Soon after the mass murders, the then Norwegian Prime Minister, Jens Stoltenberg, called for "more democracy, more openness, more humanity".

"We got to know how he had planned this, how he executed it, how he found money for it, who could have been involved, and also we were informed about the ideology of his.

"Now his crimes are being studied in schools, even some of his ideas, but in a responsible way."

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Seierstad raises concerns that the Christchurch killer could have been inspired by photos of Breivik and news stories about the case.

"The mainstream media can contribute to the fact that these people gain some kind of fame through being photographed, through being listened to after they have committed these terrible crimes."

However, she argues that terrorists are more likely to share information and cheer each other on sites on the dark web, such as 4chan and 8chan.

"That's where Tarrant found Breivik's manifesto," she says.

Seierstad says it is vital that the police and other authorities monitor online sites more carefully and contact young people who begin to post on racist internet sites.

"Tarrant and many of the shooters in America, they have announced their shooting [online] sometimes 24 hours ahead. Where were the authorities then?"

She says it was a mistake for the media to publish photos that Breivik had posted online of himself posing with a gun, because these would have been terrible for those who had lost children on the island to see.

However, publishing information about the case was important for Norwegians because "he is one of us".

"He was born in Norway, he is a fellow Norwegian - he actually lived on my street.

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"We had to question ourselves 'are we to blame for this? Could something have been done differently? At what stage of his life could this crime have been averted?'.

"For us to come to terms with this terrible tragedy, it was important to just dig really deep and try to find out as much as possible about him."

Shortly after a gunman killed 51 people and injured 40 at two mosques in Christchurch on 15 March last year, Prime Minister Jacinda Ardern said she would not speak the killer's name.

"He is a terrorist, he is a criminal, he is an extremist, but he will, when I speak, be nameless," Ardern told Parliament.

"And to others, I implore you: Speak the names of those who were lost rather than the name of the man who took them."

Ardern also said the victims were real New Zealanders, but the gunman was not.

"They are us. The person who has perpetuated this violence against us is not. They have no place in New Zealand."

However, Seierstad says it is important to remember that terrorists are people who grew up among us.

"Terrorists do have names, they have biographies and they're not nameless monsters that have nothing to do with us.

"They don't live in vacuums - they're inspired by what is happening in the society, by what they read online.

"If you treat them as something alien to the rest of us, I think it's really hard to deal with, because it's suddenly like: this is inevitable, he's different, he has no name, he's a monster.

"We have to know and try to find out at what stage could this have been averted."

The Christchurch mass murderer chose not to speak in court, whereas Breivik did for half an hour at the beginning of his trial and for an hour at the end.

"There was a very powerful moment when he was going to get his one hour. All the victims, the support group, the parents and others rose up and left," Seierstad says.

"There was actually a reaction from him then, because after 10 weeks when he had been sitting there, he wanted to have his moment."

The longest possible prison sentence in Norway of 21 years was imposed on Breivik, but he has the right to apply for parole every five years.

His imprisonment is geared towards rehabilitation, but Seierstad doubts he will ever change.

"As opposed to Tarrant, Breivik has been continuing writing letters to the press.

"He has written letters to me about his ideas, about how deeply he still agrees with what he did and he regrets not having killed more people.

"There's no way, as I see it, that this person will be let out into the society because he poses a great danger to us all," she says.