Janice Nix, who’s 67 and from Clapham, has been convicted of the manslaughter of Andrea Bernard in 1978.
Her death was treated as an accident until her older brother Desmond went to police in 2022 with a new account of what happened.
Nix was also found guilty of the assault and ill-treatment of Andrea’s older brother Desmond between 1975 and 1978.
Andrea died nearly six weeks after arriving at hospital with severe burns to 50% of her body, caused by the incident at their home in Thornton Heath.
The Coroner at the time concluded her death was a result of sepsis caused by the burns, and it was ruled an accidental death.
However, in 2022, her brother Desmond – who was eight years old at the time – came forward to police and said he believed Janice was responsible for Andrea’s death.
She’ll be sentenced at a later date.
Detective Inspector Louise Caveen, from the Met’s Cold Case Homicide team, said: “This is a particularly tragic case and my thoughts ultimately remain with Andrea’s family, whose lives were changed irrevocably back in 1978.
“In particular, I want to pay tribute to Desmond, who bravely made the decision to come forward and speak to us, as well as giving evidence at trial. It is thanks to his courage that Nix has now been found guilty and will finally be held responsible for her actions.
“I hope this case demonstrates that the Met will always review any new evidence that is brought to us, no matter the length of time that has passed. We will use all of the resources we have available to seek out the truth and pursue new opportunities to get justice for all victims who have been unlawfully killed.”
