Earlier that day Welsh had felt angered as he did not want to be treated as a babysitter for the 17-month-year-old.
According to the summary of facts, that evening the boy's mother Savanna Bell asked Welsh to watch over him while she was out.
Shortly after she left, Welsh threw Malcolm "with significant force" towards a couch while more than a metre away.
The baby hit the back of the couch, the wooden frame of which was thinly covered, and bounced onto the floor.
Malcolm was immediately unconscious and did not move.
At 7.32pm Welsh called Savanna Bell saying the boy was having a seizure and needed an ambulance.
She ran back to the apartment dialling 111 to speak to an ambulance call taker on the way.
The ambulance arrived after Savanna Bell at 7.43pm, paramedics would describe the unresponsive boy's breathing then as "slow and laboured".
At Starship Hospital doctors tried to relieve the pressure on his brain caused by swelling and bleeding.
However, a final CT scan on June 24 showed that the right side of Malcolm's brain was dying or dead.
Police were alerted to the boy's injuries by hospital staff who believed those injuries had been inflicted by another person.
Police intercepted a phone call between Welsh and Savanna Bell on June 25.
"He was fine when I left," she said.
Welsh replied: "Oh yeah course he was, aye. You tell me what happened Savanna? What'd you do to him before I even had him?"
"Nothing," she said.
In other phone calls to friends and family, also intercepted by police, Welsh blamed Savanna Bell for her boy's death.
Malcolm Bell died six days after he was rushed to hospital. Photo / Supplied
The Herald has previously reported that Oranga Tamariki had been contacted with concerns about the welfare of Malcolm before he suffered fatal injuries.
After his death the agency initially declined to comment before an Auckland manager then said they had been working to provide support to him and his whānau prior to his death.
The Herald has also previously reported the wee boy was a nephew of triple murderer William Dwane Bell.
Malcolm's maternal uncle killed three people during a drug-fuelled robbery at the Mt Wellington Panmure RSA in December 2001.
William Bell is serving a 30-year non-parole life sentence.