Police have said the starting point of their criminal investigation into the Grenfell Tower fire was that 80 deaths resulted from manslaughter.
A combination of factors led temperatures inside the block to reach 1,000C (1,832F), an inferno so sustained that some human remains are unidentifiable.
Police said detectives would examine firms, individuals and those who refurbished the block and devised its fire safety policies.
Metropolitan police assistant commissioner Martin Hewitt said on Monday: “We believe around 80 people lost their lives as a result of a fire that quite frankly should not have happened.
“The investigation we are conducting is a criminal investigation that quite obviously is starting from the potential that there was something that effectively amounts to the manslaughter of those people.”
The Scotland Yard investigation is examining the “actions and inactions” that led to the fire’s spread and consumption of the tower block, which not only killed people but consumed their bodies to such an extent they may never be formally identified.
Commander Stuart Cundy said the criminal investigation would bring whoever is to blame to justice: “You can’t listen to the accounts of the survivors, the families, and those that lost loved ones, and listen to the 999 calls, like our investigation has done, and not want to hold people to account for a fire that should not have happened,” he said.
Cundy added: “It is emotive … but it is very true.”
He said calls from trapped residents to 999 were “deeply distressing”, with one lasting 55 minutes.
Police believe the death toll will be about 80. Claims that hundreds more are missing are incorrect, they said, as for the first time they gave figures based on their inquiries that 350 people were inside the tower when the fire broke out nearly four weeks ago.
Some 255 people survived and are accounted for. Fourteen other residents were outside and away from the block. A total of 73 people have been reported missing. Of those, 32 have been positively identified, leaving 41 who can not so far be identified.
DCI Andy Chalmers, leading the effort to recover the victims, said: “The scale of the task is unprecedented in my experience.”
All identifiable bodies have now been removed. Investigators were examining debris, assisted by forensic archaeologists and anthropologists.
There has been no equivalent criminal investigation in modern British criminal history, so international expertise is being sought. Those who carried out the recovery and identification of human remains after the 9/11 terrorist attacks in the United States in 2001 have been consulted.
It is understood that some families have been told that the remains of their loved ones were so badly damaged by fire that it may not be possible to return them.
Chalmers said: “The intensity means some people may not be identified.”
Devastation in the block of flats is worst from the eighth floor upwards, police said. Chalmers said postmortems so far have recorded the cause of death as the effects of fires. Chalmers said: “There are a lot of different gases released as a result of the fire.”
Bit by bit, the full horror of what the residents experienced is emerging. Police said those trapped inside the burning block desperately sought safety.
Chalmers said: “People who were unable to escape moved around in the tower, trying to flee the fire, in many cases fleeing upwards, and drawing together.”
Police defended the fact that their investigation is yet to apply for a search warrant, make an arrest or interview anyone under criminal caution.
They said companies involved in refurbishing the block, some 60 in all, were voluntarily handing over material detectives had asked for.
Cundy said: “You will be surprised how many people or organisations hand over material that might be incriminating.”Areas the criminal investigation will look at include the advice to residents to “stay put” in the event of a fire and why it spread so quickly.
Grenfell Tower contained 129 flats, most of which were one- or two-bed properties. Police have been unable to trace survivors from 23 flats.