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The shocking past of one of Rotorua's most notorious killers is to be revealed for the first time in a television documentary tonight.

New Zealand was rocked by the unprovoked home invasion murder of Reporoa woman Beverly Bouma in 1998.

Her killer, David "Blue" Poumako, turned from a baby-faced little boy growing up in Kaingaroa with his mother and father to a remorseless killer.

Poumako, who died in prison at the age of 27 from a heart attack while serving a life sentence for Mrs Bouma's murder, is the subject of tomorrow night's Beyond The Darklands documentary series.

The show features clinical psychologist Nigel Latta as he explores the backgrounds of high-profile New Zealand killers.

Poumako's mother, from Murupara, is to speak publicly about her son for the first time. Executive producer Philly Delacey Iles said the woman was clearly still rocked over what her son did.

"They are a family who have been devastated by his actions and to this day don't understand why he did it ...

"She did her best to raise a boy to live to the standards of her and her husband."

Poumako and three others - Dillon Hitaua and young brothers Mark and Luke Reihana, went to the Boumas' Reporoa farmhouse on November 30, 1998. The motive was burglary and to steal money using their bank cards.

But Poumako took Mrs Bouma into a room and shot her.

Poumako's primary school teacher John Laing remembers him as "a likeable sort of rogue".

The programme reveals it wasn't long before Poumako started showing a darker side. He intimidated a teacher with a knife, and by 11 he was sneaking out of the family home to go drinking.

His parents learned from a social worker that their son had been an alcoholic before he hit his teens and Poumako spent time living in a Hamilton boys' home.

Sergeant Chris McLeod, who worked on the case and will feature on tomorrow night's show, told The Daily Post he had several dealings with Poumako.

His offending started with stealing cars, but quickly progressed to "ghosting" - ripping off cannabis plantations in the forest around Kaingaroa - and growing it and selling it himself.

Mr McLeod described him as a petty criminal yet someone who had leadership qualities.

"He liked to have his followers around him.

"He surrounded himself with young guys who were impressionable. He liked to be the top dog."

It was a tip-off from one of Mr McLeod's informants that lead to Poumako's arrest.

"It was a nice little break. That criminal [the informant] wasn't happy with what went down."

Mr McLeod said the group's intention was to rob the Boumas but he believed Poumaka's actions became sexually motivated. "They had no intention of killing anyone. It was Blue who went off on this power tangent. He decided he was going to have his way with her. She said 'I don't want to go there' and it got ugly."

Retired Detective Inspector Graham Bell told The Daily Post yesterday Poumako was at home making a hangi with his family the day police arrived to talk to him about the killing.

"He said he didn't know anything and told us where to go. He gave the camera [from the film crew travelling with police] the bird (the fingers). That's what he was like."

* Beyond The Darklands screens on TV One at 9.30pm tonight.