A social worker cried as she told a court how she saw Macsyna King "dump" one of the Kahui babies in a cot and roughly change a nappy.
Chris Kahui is defending two murder charges at a trial at the High Court at Auckland. The trial is beginningits fifth week.
Kahui denies inflicting the fatal injuries that killed his three-month old sons, Cru and Chris Kahui. He says someone else, probably the babies' mother Macsyna King, harmed them.
Manaaki Poto, worked as a whanau support worker and told the court she witnessed an argument between Kahui and Ms King while the babies were in the neonatal unit at Middlemore Hospital.
Ms King started screaming and swearing at Kahui to get some wipes for the babies.
"It was all one way, voices raised," she said.
She asked Ms King to "tone down" before Ms King "dumped" the baby into a cot.
"I stood in between the parents to make sure Chris wouldn't retaliate," she said.
Defence lawyer Lorraine Smith asked her to demonstrate to the jury how Ms King was supposed to have put the baby down.
Crying, Ms Poto stood and mimicked how Ms King put the child down and then described how she roughly changed his nappy.
"She just lifted it up and shoved the nappy underneath."
Ms Poto said Ms King was aggressive and defensive and Kahui was quiet and polite.
Under cross-examination by crown lawyer Richard Marchant, Ms Poto was asked why she hadn't documented the rough nappy changing.
She replied she had documented the aggressiveness but not the rough changing because she hoped to get the parents behaving appropriately.
She also denied being related to Kahui, saying she had never met him until he came into the neonatal unit.
Mr Marchant put it to her that there was a connection between her family and that of Kahui's mother. Ms Poto told the court her niece had married someone with the same surname as Kahui's mother.
