The fire which destroyed a Cornish hotel is being treated as a major crime by police.
One man died in the blaze at the Penhallow Hotel in Newquay on Saturday and police believe two people still missing may also have perished.
A police spokesman said: "It will be treated as a major crime until there is evidence to the contrary."
Police and fire investigation teams have started sifting through the debris for evidence of what caused the fire.
It is understood investigators are focusing on a specific area of the site where a body is believed to be buried.
The search of the site, which has been reduced to rubble, is expected to take several days.
Scaffolding with screens has been erected to enable the investigation to take place out of public view.
Det Ch Insp Darren Lockley, Senior Investigating Officer, said: "We don't know what happened.
"As part of our working practices we'll treat it as a major crime until we get evidence to the contrary.
"It's far more difficult to retrace your steps if you discover there is a significant crime that's occurred."
He said police and fire investigators were trying to establish a timeline of movement for individuals who visited the hotel and also the escalation of the fire.
Four people taken to the Royal Cornwall Hospital in Truro are said to be improving.
One is in a critical but stable condition and three are said to be in a stable condition.
Danger of collapse
More than 80 people safely escaped from the building.
Police believe the 43-year-old man who died fell from a second-floor window. He has not yet been named.
Two people aged in their 70s and 80s are missing.
Specialist demolition crews have already pulled down the precarious upper floors of the hotel which were in danger of collapse.
Cornwall County Council is to review fire cover across the county as a result of the blaze.
Council leader David Whalley told BBC News: "When we undertake the investigation we will look very carefully to make sure we provide the fire cover in all areas which is right for those areas."
This follows a call by the Mayor of Newquay, Patrick Lambshead, for 24-hour fire cover in the town during the summer months.
He said the number of people resident in the resort grew from about 20,000 to 100,000 over the three-month period.
Police are appealing for witnesses who were in the hotel between 1900 BST on Friday and 0100 BST on Saturday to come forward.
They have also asked that anyone with photographs or video recordings of the fire should contact the police incident room on 08452 777 444, quoting Operation Truck.