"The Crown case unravels because there is no proof that it was Troy Taylor rather than Mikala Stokes who delivered these injuries," Shamy said.
Taylor is part-way through his evidence today.
He's told the jury of six women and six men how he considered Ihaka, and the child Stokes was heavily pregnant with at the time of the death, to be his own.
Asked by Simon Shamy's brother and fellow defence counsel Phil Shamy about police asking him about his relationship to Ihaka after he died, he replied: "I don't care what anyone thinks - he was my son.
"I loved them and considered them to be my children."
Taylor also told how he'd planned to adopt Ihaka, and Stokes' second child, and that he'd also given Stokes a "commitment ring" to show that one day he would marry her.
Asked about his relationship with Stokes, he became emotional: "She was my best friend. I loved her."
The statement caused Stokes, sitting in the public gallery, also to start crying today.
Taylor told how he would do most things with Ihaka, including baths, bedtimes, and getting up to him in the night.
He told the court how he played with Ihaka often and considered him "my wee shadow".
"He used to follow me everywhere. I loved it," Taylor said.
"He gave me all the love and attention in the world. And I adored him for that as well."
Taylor told how he grew up in Mosgiel, Dunedin, and attended Taieri College before going on to Otago Boys' High School.
He represented Otago in under-16 and under-18 rugby league, Dunedin at rugby union, and the South Island at wrestling.
After leaving school at 16, he worked in an abattoir and was a member of the local volunteer fire brigade before shifting to Christchurch to work for his uncle's roofing business.
However, he told the court how he suffered several concussions playing sport and even being headbutted by a sheep.
In 2014, he was hospitalised for 10 days with a concussion, which left him nauseous, dizzy and suffering severe headaches and migraines.
However, he felt that with treatment and medication he was improving up until Ihaka died.
The Crown concluded its case this morning.
The Crown and the defence agree there were no intruders on that fateful night and that the boy's 59 horrific injuries, including broken bones, were not accidental.
The Crown says Taylor was suffering from sleep deprivation, headaches and irritability caused by multiple concussions around the time Ihaka was developing an ear infection, when he allegedly caused the fatal injuries.
Stokes, who was 36 weeks' pregnant at the time of Ihaka's death with her second child, repeatedly denied the accusations when she gave evidence last week.
Taylor also denies assaulting the child on July 2, 2015 - the day before the alleged murder.
The trial, before Justice Cameron Mander, continues with Taylor's evidence.
