By Anneke Smith of RNZ

The defence has called its own expert witness in the trial of a man accused of murdering a Mangawhai toddler.

Aaron Archer is on trial in the High Court at Auckland after pleading not guilty to murdering his former girlfriend's daughter Ariah Roberts at Mangawhai last August.

The 2-year-old had been left in Archer's care while her mother went to the supermarket and died of a blunt force head injury shortly afterwards.

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A post-mortem later identified more than 20 bruises on her body; most of them on her head.

The Crown claims the injuries can't be explained by an accident and has accused Archer of assaulting the toddler when he was left alone with her.

At the time of her death, Archer told witnesses he was swinging the girl around when he lost grip and she hit a wall before falling on the floor.

It called Dr Rexson Tse, a pathologist who completed Ariah's post-mortem examination, who told the court a single knock to the head may explain one or two bruises but not more than 20.

"These are not normally seen in children of toddler age of normal daily knocks and bumps. These are classical features of abusive head trauma therefore it is very, very, very unlikely this is from an accident."

This evidence was today disputed by Miami-based forensic pathologist Dr David Garavan, who was called as the defence's first witness.

He told defence lawyer Ron Mansfield Ariah's injuries may have been caused by being swung around and hitting her head.

"All I can do is offer an opinion as to whether the narrative you're offering me is reasonable or unreasonable and in this case it's reasonable."

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Drawing on his expertise, he said the sum of the bruises could be explained by a knock to the head, her body being handled during resuscitation attempts and regular knocks and bumps.

However, he conceded bruising around both of her ears raised "a red flag" and was most unusual in cases of injured children.

The jury has heard a longitudinal study, known to forensic pathologists, has found bruising around the ears is rare and only occurs in one in 1000 children.

Aaron Archer appears in the High Court at Auckland. Photo / Jason Oxenham
Aaron Archer appears in the High Court at Auckland. Photo / Jason Oxenham

Crown prosecutor Brian Dickey asked Garavan if he thought this particular aspect of Ariah's injuries was unusual.

"Yeah absolutely and I would require an explanation, or narrative, that would provide an explanation for it.

Dickey then asked Garavan if blunt force trauma through physical abuse of a child could explain the bruising around the ears.

"That's something you would worry about for sure."

The Crown and defence are expected to deliver their closing addresses on Monday morning before Justice Christian Whata sums up the case.

-RNZ