A mother who repetitively lied to everyone on the day her son died should be on the stand, not his father Anthony Simon Pickering.

That's the argument from Pickering's lawyer in the closing of the trial where the 32-year-old is accused of the murder of Poseidyn Hemopo-Pickering.

Baby Poseidyn was rushed to Middlemore Hospital, and later to Starship Children's Hospital on the evening of September 5, 2020, after emergency responders found him unresponsive at his Manurewa home in South Auckland. He died hours later.

Today in the High Court at Auckland Pickering's lawyer Quentin Duff closed his case to the jury, blaming Poseidyn's mother Filoi Huakau instead.

"She was the last person to interact with Poseidyn," he told the jury.

The 10-month-old baby was left alone with his father, while his mother ran errands from 2.52-3.09pm.

This is when the Crown says Pickering, who goes by his middle name Simon, caused the fatal injuries.

Huakau told police and medical staff she was the last person to have a normal interaction with Poseidyn, claiming he was breathing and looking normal at 3.09pm.

But in court, she told the jury she was lying to protect Pickering and her son hadn't woken up when she got home.

Duff said the Crown's case began, ended and failed with Huakau.

She originally told police and hospital staff on two separate occasions that Poseidyn had grabbed her T-shirt, wriggled and cried when she got home on the day he was fatally injured.

Duff, who addressed the jury via an audiovisual link after testing positive for Covid, said Huakau's initial statements were in fact the truth.

"If you accept that Huakau lied about her interactions with Poseidyn and that her new version is the truth, then you must still acquit Simon."

"This is because her evidence is still that she is the last person to interact with the baby normally after 3.09 pm."

Duff said Poseidyn's injuries could not have been inflicted before 3.09pm.

"We know this because medical expert Professor Colin Smith told the court a child would have been immediately unconscious after suffering the injuries Poseidyn did."

"We figure out when the injury happened by asking the family when they last seemed normal, it means the injury would have happened after that time."

Huakau told medical and police staff that this was at 3.09pm after Pickering had spent his 16-minutes of alone time with Poseidyn.

"We will never know what Huakau did and we will never know if it was by accident or purpose, I do not have to solve this mystery and nor do you."

"The Crown's case has relied upon three lies and CCTV footage," Duff said.

Justice Michael Robinson will sum up the case before the jury retires to deliberate.

Two jurors have also tested positive for Covid, taking the jury from 11 down to 9.