Death resulted from severe internal bleeding after the splitting of his liver by what the Crown says was an injury which must have happened in the previous hour to 90 minutes before arriving at hospital.
During that time Hapuku was in charge of the child in a sleepout at the Flaxmere home of the boy's grandparents, but, the court was told, had spent much of the day playing a PlayStation game.
Returning to the sleepout from bathing and feeding an older son inside the house, Ms Reti became concerned when she noticed the baby's changed complexion and lack of response, after Hapuku said her son had vomited during her absence from the room.
While there was no evidence of any assault by Hapuku, Crown prosecutor Steve Manning suggested he could have reacted in frustration with the child while being more focused on trying to "clock" a PlayStation game.
Defence counsel Eric Forster called expert rebuttal evidence to challenge the Crown specialists, and suggest the act which led to the injuries could have occurred several hours earlier. Mr Forster said the other possibilities had not been ruled-out.
In a 40-minute summary on the sixth day of the trial, Justice Miller also warned the jury not to take any inferences from the fact that it was a retrial.