Shahbaz Khan, 51, had been on trial for the killings of Dr Saman Mir Sacharvi, 49, and Vian Mangrio, 14, in Burnley, Lancashire, but on Wednesday he changed his pleas to guilty.
Last week, the handyman told the jury at Preston Crown Court he believed another person killed them after he left their home at around 10pm on September 30, 2020.
After his arrest he claimed supernatural spirits, known in the Islamic faith as jinns, had been responsible for the deaths.
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On Wednesday afternoon, Khan, of Ribble Avenue, Burnley, was rearraigned and from the dock entered pleas of guilty to the murders of Dr Sacharvi and Miss Mangrio, and also admitted a third count of arson being reckless as to whether life was endangered.
His wife, Rabia Shahbaz, 45, also of Ribble Avenue, denies doing an act intended to pervert the course of public justice, namely giving a false alibi for Khan, and remains on trial.
Trial judge Mr Justice Goss told jurors: "That is the end of the case as far as Shahbaz Khan is concerned. You don't need to consider his case any further.
"His wife remains on trial and you will have to return a verdict in her case."
He said it is likely jurors will start their deliberations on Thursday after hearing closing speeches from the barristers and his summing up of the case.
The trial was adjourned until Thursday.
Opening the case against Shahbaz Khan, prosecutor David McLachlan QC, had said the defendant, a former computer network engineer in his native Pakistan, strangled Dr Sacharvi and then attacked her daughter when she returned from school.
He was then said to have set fires at the property, including the severe burning of Miss Mangrio in the lounge, an attempt to set Dr Sacharvi alight in the upstairs front bedroom, and another blaze in the kitchen before their bodies were discovered on October 1.
Khan was arrested after CCTV footage on September 30 showed him visiting the home where he previously carried out various repairs including a garage conversion.
Police later found jewellery worth tens of thousands of pounds belonging to Dr Sacharvi in a loft at Khan's home - which he claimed the doctor asked him to keep for “security purposes” whenever she left the country.
Also recovered from his address was a purple Samsung phone which contained Google searches on the morning of September 30 for "obsessed" and "defined obsessed".
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