The account of a man who died while awaiting trial for the murder of his 5-year-old autistic stepson has become public for the first time, with his lengthy police interview played to a coroner investigating the boy's death.

Leon Jayet-Cole was rushed to hospital after suffering a serious head injury at his Christchurch home on May 27, 2015, and died in hospital the following day.

Stepfather James Stedman Roberts was charged with his murder. The trial was set down to begin on October 31, 2016, but he died in July that year.

Child, Youth and Family said it had worked with the family but investigations "did not establish evidence of physical abuse".

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Coroner Brigitte Windley is presiding over an inquest into Leon's death, which began in Christchurch today.

The coroner explained that the inquest will be conducted in two phases: The first looking at the cause of Leon's fatal injuries and how they came to be inflicted. This will include if police were correct to conclude that Roberts was responsible for the fatal injuries, but she stressed the coronial process is not a de-facto criminal court - and it was not for her to determine if Roberts was guilty of murder or any other crime.

The second stage of the inquest will see if the work of any agencies fell below appropriate standards of care when ensuring Leon's safety and welfare.

Today, Detective Sergeant Chris Power, who was second-in-charge on Operation Lambeth, the investigation looking into Leon's death, arrived at the Roberts' Lambeth Crescent, Northcote, home at about 3.15pm on May 27, 2015 – just over an hour after emergency services were called to reports of a child suffering serious injuries.

At the scene, officers saw "obvious plaster damage" to an internal wall. Plasterboard on the carpet suggested it was fresh damage, Power said.

Leon Jayet-Cole died in hospital on May 27, 2015 after suffering a serious head injury. Photo / Supplied
Leon Jayet-Cole died in hospital on May 27, 2015 after suffering a serious head injury. Photo / Supplied

Leon was rushed to hospital and later that day Roberts, as well as the boy's mother, Emma Roberts, were interviewed by police.

James Roberts' police interviews were played to the inquest today.

He told how Emma, who was pregnant, called him while he worked laying asphalt to say that she had to go to hospital for some checks, and asked if he could pick young Leon up from Northcote School.

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When he went to pick Leon up, a school staff member told police that when the boy saw Roberts, he "appeared to be terrified", looked at the staff member, and said, "Mum".

Roberts told police that when they got home, Leon was "a little bit out of sorts".

Leon wanted to read books in his room, which Roberts said, for a child with "Asperger's", it rang "massive alarm bells".

He also claimed that Leon vomited before he went into his room, and wobbled like he was drunk. The only time he had vomited before was when he hit his head, Roberts said.

Roberts said he was talking to workmen at the house, watching Jeremy Kyle on TV, talking to Emma on the phone, and checking on Leon every 10 minutes.

He was talking to his newly-wed wife when he heard a "bang", Roberts told police.

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"Not a big bang, just a bang," he said, waiting for tears that never came.

Emma Jayet and James Stedman Roberts. Photo / Supplied
Emma Jayet and James Stedman Roberts. Photo / Supplied

He chatted a while longer before thinking he'd better go check on the youngster.

Roberts said when he went into the child's room, he was lying on the bed, with his head on the side "in a very unusual way".

He called out but had no answer, he claimed. The boy was pale, he said: "He felt stone cold. And I thought, 'F***'."

Roberts said he "panicked a little bit" and shook the child, yelling, " Wake up, wake up!"

"So I sort of slapped him. 'Wake up!'"

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The child didn't respond and so he phoned emergency services and tried to give him CPR.

After Leon was rushed to hospital, Roberts texted his wife and said: "Apparently I saved his tiny wee life."

The inquest, which will see three of Roberts' police interviews, continues.