Donna Parangi told police that she had seen her grandson asleep in the family car with its windows down and sunroof open.
Parangi, 48, of Ruatoki, has pleaded not guilty to the manslaughter of Isaiah Neil in November 2015 by depriving him of the necessities of life and failing to take reasonable steps to protect him.
She said she'd had her eye on Isaiah while she was hanging out washing after she and her daughter returned from Kawerau with the 8-month-old, saying they left him in the car because he was sleeping.
In the High Court at Rotorua yesterday, paramedic Linda English said staff worked on the infant in the ambulance for 26 minutes before establishing he couldn't be revived.
English said when she first saw the infant on a bed in his family home she hadn't seen any signs of life but he was warm.
She thought it was strange that he was naked, as his mother said he'd been in bed having a sleep.
The baby's mother, Lacey Te Whetu, told her she'd last seen him breathing two hours earlier when she'd put him down for that sleep. He'd recently had the flu.
When English first saw the baby an older woman and man were attempting CPR, and she later established the woman was Parangi. She and other paramedics were unable to revive him.
English said when the baby's mother was told her son was dead she cried out "come back to me my baby".
His father Shane Neil didn't appear to show any outward emotion.
Isaiah's parents pleaded guilty last month to their son's manslaughter.
Earlier in the day Parangi's next door neighbour, Sharon Biddle, said she saw Shane Neil sitting on the back doorstep and a station wagon parked in the Te Whetu's driveway with the windows up.
The Crown alleges baby Isaiah spent at least three hours in the car while his grandmother and mother binged on synthetic cannabis.
- New Zealand Newswire