A woman has been found guilty of killing her five-year-old stepdaughter by punishing her in a scalding hot bath almost 50 years ago.

Andrea Bernard’s death in 1978 in Thornton Heath, south London, was treated as an accident until her older brother, Desmond Bernard, went to police in 2022 with a new account of what happened, Isleworth crown court heard.

Their stepmother, Janice Nix, 67 was found guilty on Tuesday of the manslaughter of Andrea and cruelty to Desmond between October 1975 and June 1978, when he between seven and nine years old.

Giving evidence during the trial, Bernard, now 56, told jurors he had initially said his sister’s death had been an accident because he had wanted Nix to stop beating him.

Jurors heard that on 6 June 1978, Nix was furious after Andrea had ignored instructions not to leave the house and to help clean. After hearing Nix shouting at his sister, Bernard could hear a bath running, he told the court.

“I could hear Janice shouting ‘get in the bath’ and I could hear Andrea saying ‘the bath is too hot mummy’ … Then I heard screaming and splashing.

“Then I heard the screaming stopped and I could hear Janice calling Andrea to ‘wake up’.”

Bernard told jurors that when he had entered the bathroom he had seen his sister’s limp body and her “skin falling off her”. Andrea died nearly six weeks after being admitted at hospital with burns to 50% of her body, the court heard.

Asked whether Nix had said anything about the incident, Bernard replied: “She asked me to say it was an accident … and to say that we were in the garden when it happened and that she would never beat me again.”

He told jurors he had lived in constant fear of Nix’s beatings and had not told anyone the truth about what had happened to his sister because he had feared further punishment.

Bernard told the court Nix had beaten him with a belt, bitten him, burned him with a cigarette, and made him eat cat food.

Speaking about why he decided to change his account of his sister’s death, Bernard said: “I couldn’t carry on dealing with it, so that’s what I did.

“To place this burden where it should go.”

A burns expert told the trial that a child exposed to water hot enough to cause Andrea’s injuries would have instinctively tried to get out of the bath. Prosecutors argued this meant Nix must have forcibly held parts of Andrea’s body under water.

Nix, then in her late teens, had been in a relationship with the children’s father, making her in effect their stepmother, the court heard.

Nix, who denied the charges, told an inquest in 1978 that Andrea had bathed herself and later complained of itchy legs before fainting, jurors heard.

But during her trial she admitting giving a false account of the events to the coroner because she was in a panic over her failure to supervise Andrea while she took a bath.

“On hindsight now, I see my negligence as a teenager,” she said.

She said she had not realised the bathwater was scalding hot. “All I know is that she was in distress, her legs were red, they had bubbles on them … I didn’t know how hot the water was,” she said.

Aisling Hosein of the Crown Prosecution Service said: “No matter how much time has passed since an offence takes place, the Crown Prosecution Service will always seek to prosecute perpetrators of these horrific crimes and ensure they face the consequences of their actions.”