Eight-month-old Isaiah Neil died from heatstroke after he was left strapped inside the car outside his grandparents' home, prosecutors claim.
A baby boy "cooked" inside a hot car for three hours while his parents were getting high on synthetic cannabis, a court has heard.
Little Isaiah Neil died from heatstroke after he was left strapped inside the vehicle outside his grandparents' home, prosecutors claim.
The eight-month-old was said to be "limp", sweaty and hot when he was discovered by his father, Shane Neil, in November 2015.
Neil would later tell a police officer: "We cooked the baby."
Worried about his son, the dad said he rushed him inside and woke up his partner Lacey Te Whetu - Isaiah's mum - who had fallen asleep.
Giving evidence in court, Neil said Te Whetu checked on Isaiah and found him to be "fine" and breathing, so the youngster was put to bed.
But at around 6pm, he said he woke up and checked on the baby again at the property in Ruatoki, New Zealand, according to local media.
The child was "saturated" with sweat - and despite efforts to cool him down and revive him, he sadly died, the New Zealand Herald reports.
While the Crown says he died from heatstroke, the defence has rejected this, saying there is "considerable doubt" it caused his death.
Neil and Te Whetu have both pleaded guilty to manslaughter after their little boy died at the scene near Whakatāne, jurors have heard.
They are now witnesses in the trial of Te Whetu's mum Donna Catherine Parangi - who is charged with grandson Isaiah's manslaughter.
Parangi has pleaded not guilty to the charge.
The court has heard that the trio all lived together and were smoking synthetic cannabis on the day Isaiah died, according to the Herald.
They all fell asleep, leaving the baby in the vehicle, prosecutors say.
Under questioning from Richard Marchant, prosecuting, Neil said that he had found his son inside the car, with all the windows closed.
"[He was] sweaty, wet, hot," said the father.
He added that he took the youngster inside and checked him for a pulse, but said: "I couldn't tell, I was still pretty high."
The court heard Neil then woke up Te Whetu, who said Isaiah was "still breathing", so the parents both went back to bed.
But Neil said he later discovered the unresponsive infant in his cot.
In a panic, he and Te Whetu sprinkled cold water on their son and gave him CPR, before paramedics tried to resuscitate the youngster.
Te Whetu was said to be "screaming" and "out of control".
Tragically, Isaiah couldn't be saved.
Neil told the court that "he was gone".
The court heard a pathologist found extensive bruising and an adult bite mark on the baby's body following his death.
Giving evidence, Neil denied inflicting the injuries.
Parangi's defence lawyer, Susan Gray, hit out at some of the father's evidence, saying it was a "figment" of his "imagination".
Gray has said "science is not on the side of the Crown in this case" and that asphysxia could be another possible cause of Isaiah's death.
Following Neil's evidence, Te Whetu appeared as a witness and told jurors that her mum, who was working full-time, helped her to look after Isaiah because she "wasn't capable" herself.
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The court heard Te Whetu had a drug addiction, Newstalk ZB reports.
The mother told jurors that her son felt hot when he was recovered from the car, but she thought he had been in a deep sleep.
The trial at the High Court at Hamilton continues.