The Grenfell Tower fire in London started in a fridge freezer, and outside cladding failed safety tests, police say.
Insulation on the building also failed tests and the Metropolitan Police will consider manslaughter charges.
Seventy-nine people are feared dead after the blaze destroyed 151 homes in the Kensington tower block.
The government has ordered immediate testing of the Hotpoint fridge freezer which was involved.
Whirlpool, who owns Hotpoint, said: “We offer our most profound condolences to the victims, those who have lost loved ones, homes, and possessions, and to their friends and families.”
Nine of those who died in the 14 June have been formally identified so far. Nine people remain in hospital, with three people still in critical care.
Police said the fire had not been started deliberately and the speed with which the fire spread was “unexpected”.
Preliminary tests on the samples of insulation showed it burned soon after the test started, and more quickly than the cladding tiles.
However, they both failed the police’s safety tests – which are similar to those being carried out by the UK government.
What do I do if I have a Hotpoint fridge freezer?
By Kevin Peachey, BBC News
Anyone who has a white Hotpoint fridge freezer model number FF175BP or graphite fridge freezer model number FF175BG should register their appliance with the manufacturer to receive any updates.
Generally, the model number is found on a bar code on a sticker behind the salad container in the fridge.
These models were discontinued in 2009, but 64,000 were sold between March 2006 and July 2009. It is not known how many are still in use.
Owners should ring 0800 316 3826 or visit the Hotpoint website.
Fires connected to fridge freezers and other electrical appliances are relatively common.
More general advice on registering an appliance, should there be a recall, and other safety tips are available online on charity Electrical Safety First’s page.
Some 250 specialist investigators have been deployed to find out what happened.
All criminal charges are being considered “from manslaughter onwards” including health and safety and, fire offences.
Every company involved in the building and refurbishment of Grenfell Tower will also be looked at as part of the investigation.
Det Sup Fiona McCormack said police had been in the tower “from top to bottom”, adding that next week a lift would be installed to the outside of the building.
But she did say the forensic search “may not be complete until the end of the year”.
“There is a terrible reality that we may not find or identify everyone who died due to the intense heat.”
‘Didn’t pass any tests’
Det Sup McCormack says the tests carried out on the cladding and insulation were “small scale” but added: “All I can say at the moment is they [the tiles and insulation] don’t pass any safety tests.”
The cladding, insulation, fixings and installation will be examined both individually and how they worked together.
“The investigation will be exhaustive,” said Det Sup McCormack.
“As we learn more, the scope and scale may well grow. We will look at the refurbishment. We are looking at the panelling and the entire facade of the building.”
She said she wanted to hear about anyone who was in the tower, whether or not they were meant to be in the building.
She said: “I do not want there to be any victims of this tragedy that we do not know about.
“Our priority is to understand who was in Grenfell Tower. We are not interested in people’s reasons for being in Grenfell Tower.”
She said she was concerned they did “not have the complete picture” and reassured people not to be nervous about contacting them.
“There may well be people who no one has contacted us about – who they know were in the building or have close links to Grenfell Tower.
“The Home Office has assured us that they are not interested in people’s immigration status and we are not interested in looking at that.
“What we are interested in is making sure that we know who is missing and we take every possible step to establish if they are safe and well.”
Whirlpool said it was working with the authorities to obtain access to the appliance so that it could assist with the ongoing investigations.