A medical expert has told the trial of a man accused of murdering a 15-month-old boy it is likely the child died shortly after severe head trauma.
Troy Taylor is on trial in the High Court in Christchurch for assaulting and murdering Ihaka Stokes at their home in 2015.
The partner of Ihaka's mother, Mikala Stokes, he was considered to be the boy's stepfather.
Mr Taylor's defence lawyer suggested Ms Stokes, who was alone with Ihaka for several hours on the day he died, was to blame for his death.
An ambulance was called for Ihaka about 11pm, about four hours after Mr Taylor returned home. The child died at 11.40pm.
Neuropathology professor Colin Smith told the court he did not believe there was medical evidence to suggest Ihaka suffered the injuries earlier in the day.
If the injury happened well before his death, the nerve fibres in Ihaka's brain would have been damaged, and that was not the case, Prof Smith said.
"In my opinion... both the naked eye and the microscopic pathology absolutely point towards this child going into cardiac arrest very close to the point at which the injury has been inflicted.
"There is nothing that could support the suggestion that this was an injury inflicted at some point earlier in that day, and that this child has deteriorated over a period of time."
"What I see down the microscope in this case is a very rapid deterioration in death."