Harlow fire deaths: Blaze started in the lounge area
A house fire which killed a doctor and four of her children is thought to have started in the lounge at the back of the property.
Dr Sabah Usmani and her sons Sohaib, 11, and Rayyan, six, and daughter Hira, 13, died on Monday in Barn Mead.
A third son, Muneeb, nine, died in hospital. Daughter Maheen, three, and father Dr Abdul Shakoor survived.
An Essex Police spokesman said there was "no evidence to suggest that an accelerant was used".
Dr Shakoor, who suffered severe smoke inhalation, is now recovering from his injuries in the adult burns ward of Broomfield Hospital in Chelmsford.
He was transferred there from Harlow's Princess Alexandra Hospital, where he worked, on Monday night to be close to his only surviving daughter.
Det Supt Rob Vinson, senior investigating officer, said: "Initial indications show that the fire appears to have taken hold in the lounge area which is at the rear of the property.
"The ferocity of the blaze has made the forensic work more challenging," he said.
No evidence of an accelerant has been found, police have said.
However, the investigation into the cause of the fire continues.
"We have many lines of active inquiry," said Mr Vinson, "but we really need residents and bystanders who were in the Barn Mead area as emergency crews responded and dealt with the fire to come forward urgently."
A meeting with residents has been organised for Thursday evening by police.
Mr Vinson said: "Naturally local residents are concerned about what happened and this investigation will not end until we have exhausted every line of inquiry."
The police mobile support unit is to remain at the scene for the foreseeable future.
Harlow Council has opened a book of condolence at the town's Civic Centre.
Council leader Mark Wilkinson said: "We know how hard this tragedy has hit the local community.
"This is a time when people want to show those affected that they are thinking of them and pay their respects to those who have lost their lives."