Petrol was used to start a fire in a house in Derby in which six children died, police have said.
The blaze was believed to have originated below the home's letterbox, a media conference was told.
Jade Philpott, 10, and brothers John, nine, Jack, seven, Jessie, six, and Jayden, five, all died in the fire. Duwayne, 13, died later in hospital.
The children's father, Mick Philpott, said the family had been "overwhelmed" with support from the local community.
He said Duwayne's organs had been donated to save the life of another child and made an appeal for privacy.
"Please leave my family alone. If you've got any questions or anything at all please don't come through me and my family, please go to the police.
"You're disrupting what these officers are trying to do. So please, I beg you, leave us alone and let us try and grieve in peace and quiet."
Mr Philpott paid tribute to the efforts of the emergency services in trying to rescue his children and thanked people for their messages of support.
He said: "We grew up in a community that's been through a lot of problems with violence and to see this community come together like it has, it's too overwhelming.
"Those poor gentlemen from the fire brigade, who saw what we saw - my heart goes out to them."
Derbyshire Constabulary said the investigation into Friday's fire, on Victory Road in Allenton, was progressing well.
Assistant Chief Constable Steve Cotterill said: "I would ask people to continue helping us with our investigation by checking the area where they live for signs of discarded containers which may have contained petrol.
"Please check your gardens or any hedges in your street and call us if you find anything you believe could have stored petrol.
"I am also appealing for forecourt staff to come forward if they can recall selling petrol in a container to anyone in the days leading up to the fire."
The funerals of the six children are to be held at Derby Cathedral.
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