Former All Black flung himself across car seat to save his baby's life.

French officials investigating the death of Jerry Collins believe his partner, Alana Madill, fell asleep at the wheel moments before the June crash that ended both their lives and left their infant daughter critically ill with brain injuries.

Investigators believe the All Black great woke in the back seat after the car hit a median barrier and threw himself across baby Ayla's car seat moments before a bus ploughed into the stricken vehicle.

The inquiry into the accident on the A9 autoroute near Beziers in the south of France is unfinished but authorities have pieced together the most likely turn of events.

The south of France is rugby territory, both union and league. On the night of the crash, Collins and former French stars Jean-Francois Imbernon, Jo Maso, Jacques Brunel and Bernard Gouta were on the guest list of 350 honouring Perpignan stalwart Henry Tuilagi at Les Voiles Rouges (The Red Sails) function centre in the picturesque seaside town of Canet-en-Roussillon.

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Photos from the evening show Collins cradling Ayla, and being presented with a Samoan league shirt.

Collins, Ms Madill and Ayla stayed late, most likely to around 2.20am. Ms Madill took the wheel for the drive home. Collins took a back seat, Ayla in a car seat to his right.

The 70km journey to the couple's central Narbonne flat should have taken 48 minutes. However, their late-model black Nissan Juke SUV missed the turnoff for the town. The next chance to leave the A9 motorway was 10km away, at Beziers.

The family's vehicle was just 300m from the turnoff when it veered suddenly to the left, crashing into the median barrier and bouncing back into the middle of the motorway.

A Portuguese bus, carrying 19 passengers and two drivers on a trip from Lisbon to Monaco, crashed into the car at 91 km/h, killing Collins and Ms Madill instantly. The official time of the accident is recorded as 3.10am.

Commander Thierry Duffau, the head of the police unit that attended the crash, confirmed to the Weekend Herald that investigators believe Ms Madill fell asleep at the wheel.

"Effectively she would have slept, then hit the [barrier] when she crossed the road," Mr Duffau said.

The bus skidded 100m after hitting the car before pulling up in an emergency lane. The driver, who is said to be deeply disturbed by the crash, ran to the car and found Collins' body slumped over Ayla's car seat.

He freed the infant and moved her to safety, while another driver ran down the motorway with an emergency triangle to alert motorists to the danger ahead.

Jerry Collins with partner Alana Madill. Photo / Supplied
Jerry Collins with partner Alana Madill. Photo / Supplied

Much is still unknown about the crash. Investigators say toxicology reports, which would reveal whether Collins and Ms Madill had been drinking - and how much - will be given to their families but otherwise remain private. They are also awaiting a report into the mechanical fitness of the car.

Their working theory, however, is that both Collins and Ms Madill would have been jolted awake by the impact with the barrier and have had time to see the bus coming.

"She could have slept, and then hit the barrier, and when the bus hit the car - she would have had her eyes open, that is for sure," Mr Duffau said.

At Collins' funeral, his contemporaries hailed him as a hero. Former teammate Chris Masoe said, "When you realised what was coming and you protected Ayla from the impact with your arms and your whole body over her ... you made it possible for her to have a chance. That's the man you are."

At the crash scene, firefighters found there was nothing that could be done for Collins and Ms Madill. Ayla was taken to Montpellier Hospital and placed in an induced coma. She suffered bleeding on the brain.

Alana Madill with baby Ayla. Photo / Facebook
Alana Madill with baby Ayla. Photo / Facebook

A month later, Ayla was transferred to Winnipeg Children's Hospital in Canada.

She is now nearly 4 months old, and her future remains unclear. She continues to make progress and has been discharged into the care of her grandparents, Ruth and Darrell Madill, but her doctors believe she will have ongoing disabilities.

"Ayla will need intense ongoing care," said Collins' former manager, Tim Castle.

Ayla's aunt, Nora Dureau, said the family remained optimistic about the infant's prospects.

"The hospital staff and paediatric neurologist who have examined her are extremely positive about the progress she has made and, with her age, that she could make further progress," she said.

"There is no telling how much she could improve until she is older. But as of right now, the doctors are very hopeful."

Mrs Dureau said the family had not yet decided who would raise Ayla.