An American expert in child abuse can't say whether Donovan Michael Duff caused his 9-month-old daughter's death.

But Professor Lori Frasier of Penn State University told Duff's lawyer if he was the infant's only carer that would be her assumption.

The professor, who is also a paediatric specialist, was giving evidence via audio video link to the jury trying Duff in the High Court at Rotorua where he faces a charge of murdering Maija Puhi Duff at their Turangi home on March 12, 2015.

Duff, 42, pleaded not guilty when the trial began a week ago.


The final witness to be called by the prosecution, Professor Frasier was taken through Maija's injuries by Crown solicitor Amanda Gordon, starting with two bruises found on Maija's jaw and neck. She said these were highly suspicious and typical non-accidental trauma.

Referred to a jury question, following a forensic pathologist's evidence, on whether she had concluded if these injuries were independent of other injuries the infant suffered, the professor said she believed they were.

She was unable to say what caused an injury under Maija's nose, however she also classified it as suspicious but was more definite about scalp and skull injuries, saying these were definitely caused by blunt force trauma.

She attributed the most likely cause of bleeding between Maija's brain and skull to her being violently shaken back and forth.

She was confident traces of methamphetamine found in Maija's urine would not have contributed to her injuries, nor would earlier falls. "This was not physically possible," she testified.

Challenged by defence lawyer Moana Dorset on whether Duff was responsible for his daughter's injuries, the professor retorted she had no view on who caused the injuries "But she was not injured until some time after she was returned to his care ... if he was her only carer that would be my assumption."

Asked if older injuries Maija sustained in falls could contribute to her death the professor said her opinion was that they couldn't have. Pressed, she said she based this view on evidence from two women who hadn't seen any injuries when they bathed the baby the day before she died.

She disagreed with Dorset's proposition bruises to the infant's neck were caused when she was given CPR.

The professor said she was "less clear" that a scratch under Maija's nose could be attributed to physical abuse acknowledging it could have happened in a fall or possibly by another child playing with her.

Asked if it made Duff an abusive parent because no medical care was immediately sought for Maija the professor said any delay would certainly have contributed to her death in light of her receiving an abusive injury.

Told by Justice Mathew Downs the pathologist had said she couldn't say for sure the bruise on Maija's chest had been caused by CPR, Professor Frasier said her opinion remained that it was highly unlikely resuscitation attempts caused it.

Dorset indicated no evidence will be called on Duff's behalf.

Closing arguments will be advanced tomorrow.

The judge said he'd leave it up to the jury to decide if they wanted him to sum up the case once these were completed so they could begin to deliberate tomorrow or if they'd prefer him to leave his summation until Wednesday and retire then.