Donna Cox is mass murderer Brenton Tarrant’s cousin. She grew up with him in the riverside town of Grafton in northern NSW. Donna is the only family member ready to talk about the Christchurch massacre.

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“It is hard,” she exclusively tells Sunday Night’s Alex Cullen. “I hurt more for his mother, his sister, because he was never raised like that, in that sort of environment, you know? There was no violence. No family's perfect, but certainly nothing like that. Definitely not.”

Grafton was always world famous for its annual jacaranda festival, when the trees turn a blaze of purple. However, the people here are resigning themselves to the fact it will now be forever known as the hometown of one of the world’s worst mass murderers.

Bill North is the editor of Grafton’s Daily Examiner Newspaper. “Certainly there is a sense of numbness and shock in the community,” he says. “To think that the perpetrator of such an act could have grown up here in our neighbourhood… People knew the guy growing up, he was their neighbour, and it's just horrible.”

Donna Cox says Tarrant’s are stunned by the news. “Just what he's putting his family through. He's from a very respected family. His mum [and] his dad were pretty high in the community here, and to think that their son has done something like this… they don't deserve it. They don't deserve this.”

Tarrant’s mother is a local teacher, while his father was a garbage collector and a keen marathon runner - and someone his son looked up to.***When his dad passed away from cancer a decade ago, Tarrant up and left Grafton, setting off on a seven-year trip around the world, visiting Pakistan and North Korea before landing in New Zealand.

"It's horrible to think part of his core beliefs may have started here, but I think that his motivations have developed during his travels,” believes Bill. “He's obviously chosen a place that's known to be a very peaceful, harmonious environment, and that obviously increased the amount of shock. The shock value that's come out of this, he's probably quite conscious of.”

Tarrant maintained contact with his mum Sharon. Donna knows this will be a tough time for her. “It'll wreck her. Crush her. That's her boy. I couldn't imagine what she would be feeling right now. I really couldn't. I just want her to know that we're here for her. We love her, and as a family we're going to stick by her. That's all we can do.”

Brenton Tarrant went to school at Grafton High. He was a short, chubby kid who would eventually get into fitness, becoming a personal trainer. Several classmates described him as a class clown who’d often gotten into trouble, but was well liked and highly intelligent.

As a kid, Tarrant was fascinated with guns and violent video games. He reportedly trained for the mosque attacks by playing the highly popular game Fortnite. The chilling live feed he made of the massacre as it unfolded - a heavily armed gunman firing at innocent people - looked chillingly like one of the first-person video games he loved to play.

Donna hasn’t brought herself to watch the traumatic video. “They're innocent people. They were just doing their own thing, and next minute they're not here. He didn't have the right to do that. It's just hard to imagine that he would do something like that. But I suppose people change, don't they?”

“He wasn't raised like that, but I'm not here to defend him. There's no excuses for that. I just don't know why. If I could ask him that, I'd ask him why. How could you do that?”

“That's a twisted mind right there. You'd have to be to be able to do something like that. That's not normal. It's definitely not normal. That's not him. What changed? That's definitely somebody else.”

The death toll from the massacre continues to climb; men, women and children who were mowed down in cold blood. Tarrant killed a four-year-old boy as part of his spree. For Donna, who is a mother of five, the killing of young children is hardest to accept.

“That hurts really bad. I have a little girl that's a year off being four, and I couldn't imagine anyone taking her life like that. So I can just imagine how the families, the children, the family of anybody, what they're going through right now.”

Donna says the religious hatred in the attack is particularly devastating. “I think it's sad. We have a family member who is a Muslim, [they’re] beautiful people… I like everybody; you give me the time of day and you've got my side too. I just don't understand how people can do things to people when they've done nothing to them.”

For Tarrant’s extreme actions, Donna believes he deserves the harshest of penalties. “He deserves the death penalty for what he's done. And that hurts me to say that because he is family, but for somebody who's taken that many lives of other people, it's only fair that he deserves that same thing.”

For now, Donna and the rest of Tarrant’s family are coming to terms with their feelings about the man they thought they knew and loved, but turned out to be a monster.

“There's got to be a reason why [he did it], and to be able to find out that reason would be great. But we may not know, he might not talk, I don't know.”

“I'm hurt, I'm upset, I'm annoyed with him, I'm angry with him. He had no right to do what he’s done. He didn't have any right to take anyone's life.”

Producers: Dale Paget, Taylor Auerbach & Daniel Clarke