A Sydney father whose newborn baby died at just three months old has told an inquest he's seen the infant's mother smoke ice "more times than I've seen her go to the toilet".
A coronial investigation is examining the sudden deaths of two half-sisters, known as BLGN and DG, who were three-months and 19-days-old respectively when they died in 2014 and 2015.
The father of BLGN, who is in jail, said his former girlfriend suffered a crippling ice addiction, which would keep her awake for 10 days straight while her kids were "running amok".
"I've probably seen her smoke more times than I've seen her go to the toilet," he told Glebe Coroners Court on Tuesday.
"She would sleep until her next payday from Centrelink and then off she goes to her dealer."
The father said he saw BLGN being fed from a bottle that was propped up with a blanket, and the baby being wedged between two pillows on the lounge to keep her in position, which he attributed to "laziness".
Giving evidence via audio visual link, the father admitted he didn't visit his daughter as much as he should have, but when he did the home was "a mess".
"There's never food in the house. (The mother's) not getting up to make breakfast for anyone, let alone herself," he said.
The man said he was high on ice three days before BLGN's death when he went to the mother's unit with two other men, who smoked the drug in front of two older children.
The trio then left the house but the father said he later returned to the unit and stayed with his baby "until the sun came up".
"I was laying down and she was resting on top of my heart and I sang to her 'You Are My Sunshine'," he said.
"That's the last time I saw my daughter alive."
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It was during this time that he spotted an "Asian bloke" smoking ice in the family home.
"It was weird ... he had his own little man cave in the non-messy part of the garage," the father said.
But this evidence has since been denied by BLGN's grandmother, who also blamed her own drug addiction for giving a different version of the events leading up to the child's death.
The inquest has previously heard an Asian drug dealer who came to the house the night before the tragedy put his hands on the crying baby's mouth to make her "shut up".
The coroner earlier rejected the Department of Family and Community Services' application for a non-publication order to be made on two serious internal case reports.