One Sunday in September 2022, a man walked into Croydon police station and told officers he needed to reveal a terrible secret he'd carried for almost half a century.
Desmond Bernard described how, in 1978, his stepmother had killed his five-year-old sister Andrea by scalding her in a hot bath at their home in Thornton Heath, south London.
Her death had always been treated as an accident, but Bernard, who had been just eight at the time, told officers that Janice Nix had ordered him to lie about what really happened.
He said the siblings had lived in terror of punishments doled out by Nix, including being beaten and forced to eat cat food.
Earlier, a jury at Isleworth Crown Court found Nix, 67, guilty of Andrea's manslaughter and of child cruelty towards Bernard.
Police who investigated the case are clear Nix would never have been brought to justice had it not been for Bernard's courage in coming forward decades later.
Det Con Fran Homer, from the Metropolitan Police's cold case team, said it had been "heartbreaking" to hear how he had felt guilt over what happened, despite not being in any way to blame.
She believes his decision to walk into the police station came from a place of wanting to be "the voice of Andrea she didn't have" and feeling he was unable to carry the burden of such a secret any longer.
But proving Nix's guilt would be challenging in a case where very few records survived.
Homer said that Nix had not appeared to be anxious when she arrived at the station for an initial police interview in November 2022. Initially, she replied "no comment" to each question.
"I felt like she knew what she was doing," said Homer. "As the adult's word against a child's, she thought she'd be OK."
Nix was no stranger to being in trouble with the law. She'd previously written a memoir about her past as a notorious London drug dealer known as Mama J.
She spoke to the BBC about it in 2021, describing how she eventually turned away from a life of crime to become a probation officer.
When Nix was first released from prison, about 20 years ago, she said she suffered depression when her criminal record caused her problems keeping a job.
In December 2016, Nix was invited to speak at a government select committee as a witness, describing the challenges she faced as an ex-offender in the workplace.
"I felt that society was not forgiving, even though you try your hardest to show people that you have changed," she said.
Police said, even early in their investigation, they had started to pick up on inconsistencies in Nix's story about what happened to Andrea on the afternoon of 6 June 1978.
Andrea had died in hospital on 13 July, five weeks after suffering serious burns to half of her body.
There was no police investigation and David Malone, deputy Chief Crown Prosecutor for the Crown Prosecution Service in London, said the inquest into her death had lasted just half a day.
"Dealing with homicide cases in the modern day is very, very different," he said.
"We look at all of the data we have in our telephones, CCTV, the audio. There's that wealth of documentary evidence. And of course, when you go back such a long time, witnesses pass away."
Homer said that no hospital records had been retained and described how officers had searched local museum archives to see if they could find anything related to the case. They also tried to trace former neighbours, but no-one had information relevant to their inquiry.
However, she said they had obtained a short coroner's report including an account from Nix from the time, which contained some "startling differences" to the story she now told, which she was unable to explain.
Nix was arrested at the airport in February 2025, as she returned to London from Antigua, and charged on the same day with Andrea's manslaughter and with cruelty to Bernard between October 1975 and June 1978.
Homer said Nix had seemed shocked.
"I don't think she ever thought this would catch up with her," the detective added.
Jurors at Nix's trial heard how she had initially claimed in 1978 that Andrea had taken a bath on her own, and later complained of "itchy legs" before fainting.
Nix admitted she had given a false account of the events to the coroner, but said she had been "in a panic" over having failed to supervise the little girl.
She put this down to her "negligence" as a then 19-year-old, telling jurors that she'd been busy gardening when she heard Andrea's screams and had run to her in seconds to pull her from the water.
Homer said there had been plenty of claims she made "that didn't make sense" and had been discredited by experts, including that Andrea had been able to have a conversation after suffering such serious burns, and that the bathwater had overheated due to a broken boiler.
Nix insisted in court that she had never been violent to the children, but Desmond, now 56 years old, described a very different picture of their home life with their stepmother.
He told jurors that she had regularly beaten the children, and that she had burned him with a cigarette and made him eat cat food.
He said that on the afternoon of 6 June, Andrea had told him she was in trouble for not helping clean the house.
Bernard told the court that Nix had shouted at his little sister and beaten her, and that he had heard her saying, "the bath is too hot, mummy" and Nix shouting, "get in the bath" before hearing splashing and screaming.
He said Nix had later told him that if he said it was an accident, "she would never beat me again".
Asked by prosecutor Kerry Broome why he had lied, he replied: "Because I didn't feel protected, I just wanted it to stop."
"They were in absolute fear from her," Homer said, describing the abuse both children faced as "abhorrent".
She praised Bernard as "an amazing human being" and said he had found it very difficult to see his stepmother in court "stand there and lie and try to discredit him".
Det Ch Insp Louise Caveen said she hoped the case showed that victims would be listened to, even when a long period of time had passed.
"Without [Bernard], there would have been no case, there would be no answers for Andrea."
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