Ethan Grosvenor, 27, and his mother Tracee Grosvenor, 58, were travelling home together when involved in a serious crash south of Adelaide in 2022.
The crash killed Ms Grosvenor, while the younger Grosvenor took his own life 10 days later while detained under South Australia's Mental Health Act.
Deputy State Coroner Naomi Kereru on Tuesday opened an inquest into the deaths and will determine whether the son took his mother's life.
She will inquire into whether there were safety issues surrounding the circumstances of his death.
Mr Grosvenor had a history of erratic behaviour, drug abuse and poor mental health, counsel assisting the coroner Darren Evans said in an opening address.
The 27-year-old, who was living with his mother, had returned his two children to their mother late on December 3, 2022.
Accompanied by his mother, they left to drive home at 10.05pm.
The car crashed into a tree about a 10-minute drive up the road but Mr Grosvenor only called triple zero at 1.11am.
Evidence indicated that the car was driven in a straight line towards the tree at speed, Mr Evans said.
Ms Grosvenor's body was found by paramedics cold and in the driver's seat, with rigor mortis having set in.
A witness told police they saw the car on the side of the road close to 10.30pm, with a "distressed" Ms Grosvenor in the passenger seat.
"Concerns about whether the collision was deliberate began to form, with reports of earlier violence being uncovered, and also reports of Mr Grosvenor having grabbed the steering wheel while his mother was driving," Mr Evans said.
DNA evidence confirmed Mr Grosvenor was driving at the time of the crash about 60km southeast of Adelaide and had put his mother's body into the driver's seat.
He was detained under the Mental Health Act and admitted to Glenside Hospital.
After he was taken to Adelaide Dental Hospital on December 9 for treatment, he vanished from the waiting room for 10 minutes, before returning.
Mr Grosvenor told nurse consultant Jennifer Williams that he had gone to "stretch his legs".
In evidence, she said that if she had believed it was a significant event, she would have made a report.
After further complaints of tooth pain, Mr Grosvenor was taken to the hospital again on December 14.
He asked to go to the toilet, and shortly after, a doctor who entered a stairwell saw him standing on a railing.
Mr Grosvenor suffered fatal injuries when he fell from the railing.
The coroner also heard the man had been repeatedly detained, faced charges for alleged acts of violence against his mother and was described as a man with rigid thinking who was unable to articulate his feelings.
"It seems likely that he had undiagnosed autism spectrum disorder," Mr Evans said.
Outside court, Ms Grosvenor's sister said the system had failed their family and the police had not investigated properly.
"We knew straight away it wasn't right - we were devastated," Julie Chapman said.
She was surprised the only witnesses at the inquest were two nurses, questioning why police had not given evidence.
"The health system needs to listen to families," she said.
"(Ethan) was very disturbed. His mother did nothing but love him."
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