The fire at Grenfell Tower began inside a Hotpoint fridge freezer on the fourth floor, the police have revealed.
They also said the building's outside cladding and insulation failed safety tests and are now considering manslaughter charges in relation to the fire, which killed at least 79 people, the BBC reported.
Det Sup Fiona McCormack said the police were trying to work out why the fire spread so quickly, adding that tests indicated the cladding using aluminium composite tiles and the insulation behind it was to blame.
Around 250 specialist investigators have been tasked with finding out what happened, and they will now aim to establish whether the use of the aforementioned materials was illegal and how they were installed.
McCormack said: “We will identify and investigate any criminal offence and, of course, given the deaths of so many people, we are considering manslaughter, as well as criminal offences and breaches of legislation and regulations," reported the Guardian.
The police have collected documents and materials from various organisations but are yet to question anyone, as the investigation is still in its early stages.
McCormack continued: “We are looking at every criminal offence from manslaughter onwards, we are looking at every health and safety and fire safety offence and we are reviewing every company at the moment involved in the building and refurbishment of Grenfell Tower.”
The police have been inside the tower "from top to bottom" and will be installing a lift on the outside of the building to help with the investigation, but the forensic search may not be complete until the end of the year, McCormack added.
Meanwhile, Whirlpool, which owns Hotpoint, issued a statement to say the company offered its "most profound condolences to the victims, those who have lost loved ones, homes, and possessions, and to their friends and families."
The government has ordered the model of fridge freezer, the Hotpoint FF175BP, to be tested immediately. Consumers who own one have been urged to contact the manufacturer, but haven't been advised to switch it off.
The fridge's model number is generally found on a barcode on a sticker behind the salad container; owners have been advised to call 0800 316 3826 or visit the Hotpoint website.