A deadly house fire which killed a woman and left her teenage daughter with 40% burns to her body was started deliberately, police said.
The West Midlands force said they have launched a murder inquiry after the results of forensic investigations revealed the fire to have been an arson attack.
Detective Chief Inspector Sab Johal said he believes the family home in the Tyseley area of Birmingham had been targeted "in a deliberate attack on the address".
Firefighters were called to a blaze at the house in Cateswell Road at about 5am on Wednesday.
The teenage girl remains critically ill in hospital.
Three other women and a man who were inside the house at the time of the fire are also being treated at hospital for their injuries.
None of the survivors has yet been able to give a statement to the police.
Det Ch Insp Johal said a full-scale murder investigation was now under way but inquiries were likely to take some time.
"The fire was intense and caused severe damage to the home," he said. "Given the devastation at the scene our investigation is likely to be extremely protracted."
The woman who died is in her 50s but has not yet been formally identified.