Bradford Park, Sydenham. Photo / Christchurch Star

Bradford Park, Sydenham. Photo / Christchurch Star

A teenager convicted of helping a friend take his own life says he is sorry for what he has done.

The 17-year-old, who has name suppression, pleaded guilty to the rare charge of assisting suicide after the body of a 16-year-old was found at a Christchurch park in September.

He is in custody and faces up to 14 years in prison when sentenced in the Christchurch District Court next month.

His parents, who cannot be named because it would identify their son, said he told them soon after his arrest he hadn't done anything wrong because the 16-year-old "wanted to die".

But after "time to think" behind bars, he wrote to them saying he was "sorry for all the heartache and pain he had caused, to everybody".

His mother said the letter was a "huge step" for her son, who usually blamed others for his situation.

She thought he was starting to "get it", but would have to see him before she could be sure. "In my heart I know he is changing," she said.

She and her husband felt "extremely sorry" for the family of the dead teenager, who had been searching for their son in the days before his death.

"I would like to give my commiserations to his father," the 17-year-old's father said. "It's very sad. It's a great waste of life.

"We are going through just as much hell. Well, not quite as much, we still have our boy, but it's affected us," he said.

"No parent should have to go through what they are going through," his mother added.

The 17-year-old's parents said their son had caused problems for years. He was kind, generous and helpful when in a good mood, but had an anger problem and could lash out or become abusive.

As a schoolboy, he had learning disabilities and no respect for female teachers.

"He had a lot of problems at school ... with bullying," said his mother. "He's always been a sheep. Someone would tell him to thump someone and he would do it."

The teenager spent time in social welfare care when his parents could not deal with him, and got "mixed up" with other youth offenders.

He also spent time on the streets. His parents said he showed signs of improvement after three months at a youth justice residential centre, but things went downhill again after he got out.