Detectives investigating the deaths of a "perfect" family said a mother and her two young sons were stabbed.
It is believed Richard Smith, 37, murdered his family before killing himself in a fire at the house in Pudsey, West Yorkshire, on Friday night or in the early hours of Saturday.
Police said they were able to pinpoint the time of death because the elder child's advent calendar had not been opened on Saturday. On Friday the family, including Ben, nine, and Aaron, one, had attended a local cricket club function. They were found with their mother Clair, 36, and father, on a double bed in the burnt-out main bedroom of their detached home on Sunday by relatives.
Mr Smith, a shopfitter, died from smoke inhalation after apparently setting light to a mattress.
Mrs Smith and baby Aaron died from chest wounds, while the older boy, who was also stabbed, suffocated.