Chris and Cru Kahui were 84 days old when it happened.
Someone close to them - someone who should have been protecting and loving them - either picked them up and hit or threw them against a hard surface or shook them violently.
The boys suffered traumatic brain injuries, the result of severe impact forces to their tiny heads. They died later that week after all efforts to save them were exhausted.
To this day nothing more is known about how the twins sustained their fatal injuries or why.
The Crown maintains the twins' father Chris killed them. The coroner ruled he was the only one that could have hurt the boys, they were in his sole care when they were injured.
Kahui's lawyers have pointed the finger at the boys' mother Macsyna or her brother Stuart King who lived with the couple. He still maintains his innocence and has never been convicted of any charges relating to the boys injuries or death.
While we may never know conclusively what happened to Chris and Cru, the 2012 coroner's report sheds light on what the babies went through in the hours after they were violently assaulted.
Coroner Garry Evans, after hearing evidence from the twins' parents, wider family, police, medical experts and many others, ascertained that the Chris and Cru were "normal and well" at 1pm on Monday, June 12, 2006.
King and Kahui fed their babies together at 11am. By midday they had had a blazing row and King left the property just before midday.
Kahui's cousin April Saunders arrived at the house shortly after and told the inquest that there was no sign of any injury - new or historic.
She helped Kahui feed the boys again just after midday. She fed Cru while Kahui gave Chris a bottle.
The babies were then put to bed. No one heard them cry and they slept constantly.
At 8.40pm Kahui was having a cigarette on the front doorstep of the house with his father Banjo, who had arrived earlier. Kahui's sister Mona and her partner Stuart, King's brother, lived at the house and were also having a smoke.
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During the cigarette Kahui's 13-month-old son Shayne called for his father. Kahui went inside and the inquest heard he was in the house on his own for a period.
Mona told the inquest that she went into the twins' room about 10 minutes after finishing her cigarette. Kahui was in there cuddling baby Chris.
He asked her to pick up Cru and she noticed that his face was "starting to turn pale."
"His eyes started to roll back and his lips started to go purple," she said.
Kahui told her "he gets like that when he's tired".
Mona realised that Cru had stopped breathing, passed him to her brother and ran to get Stuart. She was scared.
Stuart came in and took Cru off Kahui. At the murder trial Stuart told the court the baby's lips "were like a dark purple. They kept getting darker and darker and darker. His body was so flimsy and so limp you could tell (it) wasn't normal."
"For about five to 10 minutes he was just lying in my arms lifeless ... (Cru started to breathe) in short bursts like he was trying to suck in air ... like sucking a drink through a straw."
Every time little Cru tried to open his eyes they would roll back and his hands shook every time he tried to take a breath, Stuart said.
At one stage he thought the boy had died.
At the trial Kahui admitted giving Cru CPR and said the infant "came normal after that".
He said he was "freaking out" and "really frightened ... really afraid". He thought his baby was dying but decided not to call for an ambulance. Instead, he sent his sister and father to find King.
Stuart told the inquest that everyone at the house wanted to call 111 but Kahui refused.
"Chris wanted Macs back," he stated.
Nothing was done to help Cru that night. Kahui slept in the twins' room to make sure the boy "was still breathing" while his father looked after Shayne.
At 9am on Tuesday, June 13, 2006, Kahui rose and checked on the twins. In a police interview he said at that stage he noticed bruising on Chris' face. He took no further action, instead leaving the house to get petrol for his car, withdraw cash from an ATM and purchase baby formula.
King arrived home at 9.35am. Her partner was still out.
She checked the twins - both were breathing and appeared to be asleep. She spoke to Stuart who told her what had happened the night before.
Kahui arrived home minutes later and was confronted by King.
"What the f*** was happening while I was gone away and how the hell did our boy get that new bruise on his face and what the hell happened?" she screamed at Kahui.
King decided to take the twins to the doctor - but not before a trip to McDonald's for some lunch. King and Kahui, joined by Stuart and his daughter Cyene and another child ate their fast food and then took the babies to the doctor at 1pm that day.
Dr Gopi Nayar at the Otahuhu Family Medical Centre saw the boys. He immediately noticed a "large" and "obvious" bruise on Chris' cheek. Kahui told him that Cru had stopped breathing the night before.
Dr Nayar told the police that he knew "straight away" that Chris was "neurologically very unwell". He asked Kahui and King if the babies had been dropped on their heads. He called Middlemore Hospital and arranged for the babies to be seen by medical staff.
Kahui and King left the medical centre and got into their car. Kahui was driving, but did not go to the hospital. He said he didn't want to.
They returned home, stopping briefly so King could buy nappies, at about 2pm. Stuart told police that his sister was "swearing, going off her face" as she collected the twins' medical books.
"She was upset, crying, swearing," he stated.
As King prepared to take her babies to hospital, Kahui walked out. He did not return and King took the boys to hospital by herself. At the time Kahui felt "picked on". His sister was "nagging" him about the state of the house; his father on his back about his relationship with King and she was "in his ear" about what happened to the babies.
He was upset and needed to "cool off", so he left.
At 2.37pm King arrived at Middlemore's emergency department carrying the babies in their carseats.
Chris and Cru had no chance. They died five days later after medical staff withdrew life support. They were 90 days, exactly three months old.
If you see or hear about a child whose safety and wellbeing is in immediate danger, don't wait, and don't assume someone else is acting.
• Call police on 111 or Crimestoppers anonymously on 0800 555 111.
• You can also report any suspected child abuse, neglect, harm or maltreatment to Child Youth and Family on 0508 326 459.