Dr Abdul Shakour, who lost his wife and four children in a suspected arson attack on their home in Harlow, Essex, "fought hard to save his family in appalling conditions", Assistant Chief Constable Gary Beautridge said.
Dr Shakour is being treated in hospital for severe smoke inhalation and severe shock, but is desperate to assist police with their enquiries, Beautridge said.
Dr Abdul Shakour suffered minor injuries in the blaze, but his wife Sabah Usmani, who is also a doctor, sons Sohaib, 11, and Rayan, six, as well as 13-year-old daughter Hira, died in their end-of-terrace house in Barn Mead, Harlow, Essex, at about 1am.
Dr Sabah Usmani with her five children
A third son, Muneeb, nine, and daughter Maheen, three, were rescued by fire crews and taken to hospital in critical condition, although Muneeb later died at the Princess Alexandra Hospital.
Beautridge said: "In the history of Essex Police, seldom has there been an incident of this gravity, in which five people, four of them children, have lost their lives.
"I would like to stress that the father of these children was in the property at the time and fought hard to save his family in appalling conditions.
"Our work with Mr Shakour to establish some of the facts of this case will, inevitably, take time because of the emotional trauma he has suffered at the loss of his family. His condition is described as stable."
At a press conference in Harlow, police asked for information about what is being treated as a suspected arson attack.
Beautridge said: "We do believe the answers to this inquiry lie within the community of Harlow."
Investigators are interviewing neighbours and speaking to members of the local Muslim community. Chief superintendent Luke Collinson said the family were "well-known in the local community", with children at local schools and members of Harlow islamic Centre.
No motivation has been given for any attack, and police say they still do not know what started the fire at the house, or what caused the fire in a burnt out car found close to the house, which does not belong to any family members.
When asked if police were considering the possibility of a race attack, or a local feud, investigators said they have "no information or intelligence to suggest this [fire] is linked to the minority ethnic community in Harlow."
Police say Harlow fire could have been started intentionally, but there is no evidence to suggest the crime was racially motivated.
Beautridge said a large number of specialist officers would be rigorous and methodical in their forensic investigation of the scene. "We will leave no stone unturned," he said.
It is understood the father was inside the house when the blaze started but had escaped by the time firefighters arrived. He is not currently being treated as a suspect, police said.
Firefighters called to the scene described the house as being "100% well alight", with flames coming from the front and back doors.