A wealthy antiques dealer has admitted the murder of his seven-year-old daughter, dramatically changing his plea on the third day of his trial.
Robert Peters, 56, throttled Sophia with a dressing gown cord while alone with her at his £1 million family home in south west London last November.
Afterwards, he called 999 to report what he had done and the child was rushed to hospital but died the following day.
The killing came just over a month after depressed and suicidal Peters was found not to be a risk by a child protection team.
Peters had admitted manslaughter and changed his plea to murder on the third day of his trial at the Old Bailey.
Previously, he had claimed he was hearing voices as well as suffering from depression.
Mr Justice Edis adjourned sentencing until Monday to set a minimum life term.
The trial had heard Peters had recently ended a two-and-a-half-year affair with a married woman and was worrying about his finances.
He waited until his wife had gone out before he woke Sophia up in bed by tying a cord around her neck and throttling her for up to half an hour.
When she asked him what he was doing, Peters said "sorry" but carried on as she struggled, the court heard.
When officers arrived at his Blenheim Road home, Peters calmly told them: "She's upstairs. I've strangled her."
Sophia was found lying in a foetal position on a single bed wearing a nightie and knickers with a black fleece dressing gown cord wrapped and knotted tightly round her neck.
She had a weak pulse and was rushed to hospital, joined soon after by her mother Krittiya, who was escorted there by police.
Sophia was treated in intensive care but died from brain injuries the next day, on November 4 last year.
Following his arrest, Peters said he had been suffering a "breakdown".
He said he had been thinking of killing his wife and family for several weeks so they could be "spared the pain and upset when he became bankrupt".
However, inquiries later showed Peters' Kensington-base oriental antiques business was not in trouble and he had money in the bank.
Peters told police he had been visited by a child protection team and feared Sophia would be taken into care.
But an assessment had already concluded on September 27 that he was not a risk to himself or others and the case was closed.
In the months before the killing, Peters searched the internet for "serial killers", "treatment of child killers in prison" and "premeditated murder", the court heard.
He picked the opportunity to kill her before she was due to return to her £5,000-a-term boarding school after the half-term break.
Sophia's mother - Peters' third wife - and other family members sat in court as he admitted murder.
Detective Inspector Helen Rance, of Scotland Yard, said: "Sophia was an innocent seven-year-old girl, much loved by her mother, brother and friends. She was tragically murdered by the hands of her own father in the most frightening way.
"Sophia had her whole life ahead of her, which was taken away so cruelly in an act of pure selfishness. Robert Peters has shown no remorse for the murder, and initially maintained a defence of diminished responsibility. However, due to the strong evidence against him, he has changed his plea to guilty.
"This was a particularly traumatic case to deal with for all concerned, and I hope that this conviction brings a degree of closure to Sophia's family."