The police announced themselves with a sharp rap on the door. Maxine Bennell knew what they were about to say. Her son, Jayden Stafford Bennell, had been in Western Australia’s Casuarina prison for nine months and had never before missed their weekly phone call. Something was wrong.

It was 10.48pm on Wednesday, 6 March 2013. Maxine Bennell slipped past the flyscreen to stand on the veranda; she didn’t want to let the police inside. They had bad news, they said. Jayden was dead. He was 20.

Speaking to Guardian Australia in a small conference room at a community legal centre in Perth in October, Bennell was still stuck on that veranda. She had spent the past 31 months trying to make sense of what the police told her.

“I am still standing on the veranda,” she said. “Ten forty-eight. That’s still stuck in my mind. Ten forty-eight. That’s when the police came to tell me my son died.”

He had died about seven hours earlier – between 3.30pm and 5.30pm, according to the autopsy. Anna Copeland, one of Maxine Bennell’s lawyers, and the supervising solicitor at Southern Communities Advocacy Legal Education Services, said it could have been even earlier. He was unaccounted for between about 1.30pm and when he was marked absent at the 3.15pm muster. He was found in an area opposite his cell, which was on the ground floor of Block D, one of the open-air blocks that surround a central quadrangle at the prison, at 3.45pm.

The autopsy report put his cause of death as hanging, and police told his mother he committed suicide, but she doesn’t believe them. Among the documents stacked in manila folders in front of Copeland is a sheaf of handwritten questions running to 20 pages listing and everything Bennell wants to know – a forensic pulling of loose threads. Why did it take so long to find him? Why was the only security camera not working that day the one pointed at that spot? And why, after the discovery of her son’s death, did it take seven hours to notify her?

Because Jayden died in custody, his death was subject to a coronial investigation and will receive a public inquest. But the coronial process is a long one and access to information is restricted. Bennell was allowed to read a summary of the coronial brief into her son’s death in April, but she had to do so in the coroner’s office and was not allowed to make copies.

Her lawyers received the full brief just 11 days ago (32 months after Jayden’s death), ahead of their first court date on Monday. That court appearance set the date of the inquest – which will be held at the central law courts in Perth on 10 and 11 May 2016 – two days before his birthday.

Counsel for the family, Steven Castan, submitted to state coroner Ros Fogliani that it would require at least eight days to properly examine all 16 witnesses.

Bennell and her ever-growing list of questions are ready.

“I’ll give the police the biggest mob of questions. Biggest mob,” she said.

Jayden was the second-eldest of her eight children. His twin brother, minutes older, was stillborn. Maxine Bennell’s grief for that loss was profound – it was one of the reasons Jayden rarely had birthday parties.

“I had never been to the cemetery, because I was waiting for 21 years to go past,” she said.

That is why she finds the suggestion of suicide hard to believe: “My son would never, never make me go sit at the cemetery.

“Twenty-one years I was waiting,” she said. “My son died two months and one week before I was meant to go sit at the cemetery. And when he turned 21 I was sitting there for both him and his brother.”

In the years since Jayden Bennell’s death, three more Aboriginal men have taken their lives in Casuarina, the latest just seven weeks ago. The prison was the site of six of the eight Indigenous deaths in custody in WA since the beginning of 2013. The inquest into the most high-profile of those deaths, that of 22-year-old Yamatji woman Ms Dhu, who died of a severe infection in police cells at Port Hedland on 4 August 2014, retired part-heard two weeks ago. Like Ms Dhu’s family, Maxine Bennell has been left wondering what has changed since the royal commission into Aboriginal deaths in custody in 1991.

Jayden had been in and out of custody since he was 14. His first stint at Perth’s Banksia Hill youth detention centre was, according to his mother, for stealing a texta. His history reads like a case study for Indigenous overrepresentation in custody: jailed young and often for crimes at the lower end of the scale.

“I don’t even know how many sunsets my son has seen,” Maxine Bennell said.

“I used to teach my boy that as long as you got imagination, you can go anywhere,” she said, recounting one of their weekly phone calls when he was in jail. “I used to say to him, like on New Year’s Eve, ‘where are you going tonight?’ And he’d say, ‘Mum, I’m going to town’.”

The rates of incarceration for Indigenous teenage boys in WA are among the worst in the world. According to a report by Amnesty International this year, one in 77 Aboriginal boys aged between 10 and 18 is in custody in Western Australia, and young Indigenous people are 53 times more likely to be incarcerated than their non-Indigenous peers. Aboriginal people occupy 78% of the cells in youth detention centres, despite making up just 3.1% of the state’s population.

When Jayden was sentenced the last time, he was 19. A district court judge ordered he serve the mandatory two years in jail for triggering WA’s three-strike laws, as well as a car-stealing offence. Under the three strikes legislation, the court is required to sentence anyone convicted of aggravated burglary offences on three occasions to two years’ jail. That law was expanded this year.

Jayden had been out of detention for just a few weeks when he was picked up, and would have been eligible for parole after one year, but his mother always told him not to take parole – better to serve your time and be in the clear than to have the conditions of parole hanging over your head and risk being thrown back in.

He seemed to be maturing, his last few months in jail. He never wanted his younger brothers to visit him in detention, lest they got ideas to join him.

He was a good kid, Maxine Bennell said. He just had a habit of getting into trouble when alcohol was involved. She is worried the inquest, and subsequent media coverage, will cast him as just another Aboriginal kid in jail, not as the grandson of Eddie Bennell, the Aboriginal leader, playwright and boxing champion who chaired the national Aboriginal consultative committee. Not as a proud Bibbulmun man. Not as her son.